If I were to take a wager, it probably was just as a trigger for the bad endings (though unlike the first game, the threshold is pretty high), at least initially. There are a few ways to take advantage of them, like moving your units with Fist/Spear skills without relying on enemy positioning (IIRC this is even required in one of the Dark Word stages, if you're not exploiting bugs like throwing past no-entry panels), healing your units with regular attacks if they happen to be standing on a reverse panel, farming weapon mastery (the stage 11-3 "Death to Cowards" is well known for that), farming skill mastery (though you usually want multiple Attack+1 geo panels along with it), raising your bonus gauge if there are no better targets, raising your combo/"standing-still" bonus (best with tanky units and a high counter stat) and maybe a few others. Not something that comes too often (especially the later ones I mentioned), but I'm glad it's an option.

Originally posted by neemoos:

If I were to take a wager, it probably was just as a trigger for the bad endings (though unlike the first game, the threshold is pretty high), at least initially. There are a few ways to take advantage of them, like moving your units with Fist/Spear skills without relying on enemy positioning (IIRC this is even required in one of the Dark Word stages, if you're not exploiting bugs like throwing past no-entry panels), healing your units with regular attacks if they happen to be standing on a reverse panel, farming weapon mastery (the stage 11-3 "Death to Cowards" is well known for that), farming skill mastery (though you usually want multiple Attack+1 geo panels along with it), raising your bonus gauge if there are no better targets, raising your combo/"standing-still" bonus (best with tanky units and a high counter stat) and maybe a few others. Not something that comes too often (especially the later ones I mentioned), but I'm glad it's an option.

is there any way when to use attack team option ?

Originally posted by Spirit Link:

is there any way when to use attack team option ?

Do you mean "anyway to guarantee a team attack"? I don't think so, but you can raise your odds of a team attack happening. Which characters you use in a team attack (Sinners and Gunners are pretty good for that), which weapons they are using, whether or not they are in a Master/Pupil relationship, whether they moved or performed an action prior to the team attack, etc. all influence your chances. You can follow this table from Prometheusx303 to know what your (base) odds are:

https://gamefaqs.gamespot.com/ps2/930240-disgaea-2-cursed-memories/map/5261-team-attack-table
(edit: forgot to mention, but this was made for the original version, so it doesn't list the characters exclusive from the remakes)

Lastly, if you want to guarantee that multiple units share EXP/Mana, you can use tower attacks instead.

edit 2: Oh, I think I know what you meant. Something like "disabling friendly fire". Unfortunately, no, there's no option for that.

gives this game a tiny bit of strategy

It prevents you from using AoE moves in some situations to require some smarter placement of your units.

I don't remember the endings in D2, but in D1 you also get different endings for killing too many of your own units.

Originally posted by lPaladinl:

It prevents you from using AoE moves in some situations to require some smarter placement of your units.

I don't remember the endings in D2, but in D1 you also get different endings for killing too many of your own units.

Or I can attack my own team to heal them when they are in reversed damage square

reverse dmg square next to each other : grind weapon mastery by hitting each other over and over.

Srsly tho, you can use this mechanic in multiple ways. Triple/tiger strike with a weak ally to move another from a dmg square (dont do this for a deathblow panel, you'll die either way).
Reduce their counter #
grind mastery/spell/skill exp.
get them low to proc their passive ability
force you to not go mad with AoE attacks.
there are 3 ending directly linked to this (Killing Rozalyn + 100 ally, Killing less than 100 ally and not killing Rozalyn, killing no ally at all with no other major ending trigger). if you're not a completionist or speedrunner, don't put too much thought into it,
Actually killing allies is also a source of xp... as crazy as it sounds. I think it's worth 1/4 or 1/8 of the actual value tho... not sure.
Healer get xp from healing... not as reliable but still. dmg then heal. rinse, repeat.
Some challenging stage, dark sun stage, you need to actually watch out for that since you only have 1 turn, x amount of summon, a weird panel or something else along these lines.

I'll just repeat this one with better details:
The very worst "win" ending requires you to actually kill Rozalyn at least once with Adell, Kill a high number of allies total(over 100 is safe number) and have 99+ felony (they need to be active I think, so no purging the sins or wtv)
lvl 1000 tink override this one so... don't kill last boss with lvl 1000+ Tink okay?