I don't think I have... but I could be forgetting a time where I did. To my memory, adapter cards have always been screwed in (or at least secure with whatever plastic latch mechanism the case provided), storage and optical drives have always been screwed into place, and so on.

It's important that your PSU and Mothers be secured properly. In most PC Cases that offer metal for where the Motherboard and PSU mount, tbis helps with linking a ground between PSU and Motherboard. Without a good ground you can end up with noise in your audio and other problems. Also on many Cases, they come with cheap wiring for the front panel connections, which means those audio connections are often unshielded and can leak in digital noise.

If you use a non metal Case such as Wood for example then it's important to connect a custom ground wire between the PSU external housing and a Motherboard stand-off to provide the ground that a metal Chassis would provide

No. Even back in the days of Apple ][ and installing hardware with chip sockets & ribbon cables, everything was still secured.

Every screw is screwed down, every cable is zip-tied, etc.