• Wind/rain cannot affect a golf ball's shot for whatever reason. Shocking I know, but I tested it quite recently with max settings and a putter and I felt absolutely no difference in trajectory.
  
• If a golf cup isn't planted underground, a golf ball will more than likely hit off the side of that, so keep that in mind.
  
• A golf cup can NOT be put in mid-air. However, you can put an Echo Block under one to make it appear that way.
  
• Golf Cups can be used as ways to activate mechanics.
  
• Golf Balls count as projectiles, so they can activate Teal Pressure Pads.
  
• Conveyor Belts can move a golf ball, too.
  
• If you don't allow scouting on your courses, or even if you do, giving your player a pair of Binoculars is generally a really good idea.

• Regular grass and Hallowed grass can be mowed by a lawn mower, which when applied will help roll the golf ball further.
  
• However, un-mowed grass will slow a golf ball down slightly, and the weeds that it grows will definitely slow it down more.

If you want your course to have a more organized look while retaining the properties of the latter, planting any kind of flower on mowed or grass that is not mowed will produce the same effect.

• Flowers used to make dyes, flowers from the Fairy Boots, flowers from flower/plant seeds, any of it will apply the same slow-down as a weed collection would. It also won't matter if the flower is in bloom or not.

That also means you can use Clay Pots as a way to make flowers elevated by one block, but have its flower still slow you down. The same also applies to Planter Boxes, which are the only "soft platforms" in the vanilla game that I could find.

• Also, vines from dirt blocks placed above WILL slow down a golf ball too, as will placed Cobwebs.
  
• Finally, matured Shiverthorn on Ice Blocks perhaps give the biggest impact, especially if there's multiple of them.

• Hard Blocks - stones, bricks, etc. If it makes a "hard" sound when you mine it, it probably counts as a hard block. They really help with making a golf ball roll and bounce, and are perhaps one of the safer options to land on. Echo Blocks and Conveyor Belts also count as these.
  
  
• Soft Blocks - like pure dirt, or snow, or ash blocks. If it makes a "soft" sound when you mine it, and can be put in mid-air, chances are it's soft. These will slow a golf ball down even more so than grass with flowers.
  
  
• Slime Block - regular, blue slime blocks. At least from my research, and I could be wrong, these are an in-between of "soft" and "very soft". As in, they'll limit rolling and bouncing quite a bit.
  
  
• Very Soft Blocks - like sand, silt, or slush. If it can't stand on its own, chances are it's very soft. The classic sand pit in golf, these will slow a golf ball down a lot. You'll almost always need a wedge to get out of this.
  
  
• Bouncy Blocks - Silly Balloon Series and Pink Slime Blocks. As expected, golf balls will bounce off of these a lot more, with more speed returning more bounce.
  
  
• Frozen Blocks - Ice Blocks and Frozen Slime Blocks. Blocks from Ice Rods also count. These will reduce a golf ball's traction, making it slide more on these blocks. However, watch out for planted Shiverthorn on ice blocks.
  
  
• Sticky Blocks - Honey. Even worse than "very soft," these will stop a golf ball right in its tracks and WILL require a wedge.

• Water - Shallow water will definitely slow a golf ball down, though it's also impacted depending on the block too. Get that wedge. If the water is too deep, get the golf whistle.
  
• Lava - For whatever reason, it isn't as bad as water in general, but still will burn those without equipment/god mode.
  
• Honey - get the golf whistle. even shallow honey will stop you right in your tracks
  
  Also, since Bubble Blocks can separate liquids but can be passed through, you can use those to make some bizarre pits. I'll edit this bit if I find any more pass-through blocks that can do that.

Platforms can act as a one-way door for golf balls -- they can come through one, but not through the other.
However, you can actually make them be able to pass through if you place a platform hammered like a stair under a platform. There's a better image on the Terraria forums post that I'll link at the end of this, that I couldn't put in this guide.
Also, if a platform is shaped like stairs, they can even hit and bounce off the stair end.

However, platforms aren't the only, well, platforms you can use. Certain furniture can also be used as platforms:

• Tables
  
• Work Benches
  
• Pianos
  
• Dressers
  
• Crates
  
• Bars (such as Silver Bars, gold bars, etc)
  
• and once again, Planter Boxes

ALL platforms count as "hard blocks," no matter what they belong to. So, even Honey and Frozen platforms/furniture count as hard.
The only exception to this, however, is the Planter Box, which counts as a soft platform. However, as it grows flowers even without a seed, make sure to freeze time if you don't want a flower there for whatever reason.

• Boulders/Rolling Cacti, when at rest, count as hard blocks that aren't even sloped. However, if in motion from a player messing with it, they'll pass right through a golf ball.
  
  
• And again, vines from dirt blocks/cobwebs can also slow down a golf ball. Alongside that, Bubble Blocks can also be used to separate liquids but allow a golf ball to pass through, meaning more interesting liquid pits for golf balls.

Golf Balls cannot:

• Interact with enemies
  
• Interact with portals
  
• Interact with minecart tracks
  
• Be affected by anything hanging that's not vines/cobwebs
  
• Be affected by wind/rain
  
• Be affected by moving Boulders/Rolling Cacti

This is a repost of my "golfing properties" post from the Terraria forums, ported to Steam for exposure.
https://forums.terraria.org/index.php?threads/golf-things-you-may-or-may-not-know-about-course-building-v0-1.94641/

Credits to Khaios's map, "Putt-raria!", for the inspiration.
...and you, for reading!