Does "Invisibility" do anything useful?

[Taem]

So I cheated a bit and looked up the Grimrock Complete Spell List. Sue me. Anyhow, I was getting slaughtered on level 6 doing the Fighter Challenge with my two archers up front and two wizards in back, so I figured, "hey, Invisibility should work great here... only reason I went Air instead of Fire. Frakin spell does not work worth a damn! As soon as you get near the statue, you are teleported and stupid little critters destroy my party, nary caring at all that all four of my toons had the "invisibility" icon on their portrait. So I decided to come back and do this challenge later when I've gathered a bit more experience.

Cool story bro, I know, right? So here I am descending to level 7, assuming that was part of the Fighter Challenge, I cast Invisibility again before descending the stairs, and lo and behold, a green slime is just waiting for my ass on the block before the stairs... and he also does not give a shit that I'm supposedly invisible, freely attacking me. And no, I did not attack with any of my toons, nor cast anything.. hell, I didn't even move, but that does not stop these monsters from deciding invisibility is borked in this game. So when is this spell actually useful?

EDIT: Just saw another thread on this. So it's assumed light sources may play a factor, however monsters can still see you if standing next to you? Does not help for the purposes I needed it for whatsoever. My main playstyle with two archers and two mages is kiting the enemy from range. I'd only use invisibility to sneak up/through a pack of dangerous foes to get to a safe spot to take them out. Now... I wish I could respec my air mage to a fire mage had I of known this.

[Asteroth]

Yup, all it does is help you sneak up on the enemy or avoid a fight. Enemies still immediately notice you when next to them.

It can be handy for getting a position to backstab, really I'm pretty sure that is the main use. But also if you're not confident you can win a fight it will help you run away or slip by since it effectively is lowering the enemies range of vision.

[Dr.Disaster]

Invisibility does only one thing: others can't see you and the less light there is the better. What it does not is making you undetectable by other means than eye sight and with the more light going it's harder to go unnoticed. Even then if a monster attempts to run into your party's square (because it did not see you due to Invisibility) it does not stop it from attacking thin air because for some strange reason it can't enter a seemingly unoccupied square. As for the mentioned example: by logic Slimes have no eyes so they detect players by other means, making Invisibility utterly useless against them.

The same applies pretty much to players. I have come across mods using invisible walls which i had to bump into to see if there is a way around or not. Now add the option of breakable invisible walls and you will also hack away at thin air trying to see if they give way.

[Komag]

I always felt that invisibility was hardly useful because of how short lived it is, so now one of my armor sets grants continually refreshing invisibility, very nice!

[MostlyHarmless]

just finished the game. my mage specialized in air and ice magic with some points in spellcraft - my spells of choice were light and frostbolt. invisibility helped a little bit in the final boss battle (although some mobs still spotted me), but overall i didn't use it much. i think it might be useful for someone with an assassin rogue in tow or for someone who wants to skip combat and rush through the game, but I didn't find myself using it much. in hindsight i should probably have specialized in ice only, with some point in fire and spellcraft. that said, i probably could have used invisibility more to find a good strategic spot before enging in battle in some of the trickier spots of the game.

[Isaac]

I liked the invisibility spell in "Eye of the Beholder"; I didn't much care for the way it was in LoG. In EOB, the spell made the target invisible for the duration, or until they attacked.

This also meant that the mage could turn a wounded PC invisible, and make them far less likely to get hit, except for area effect spells.