Indeed, but if you are walled off then LEMISI is the only thing besides ENDISWALL. And not just if you're walled off - there are places where the exploration is unreachable because of the unpassable terrain. Grabing one early in Ick Swamp is a godsend, it makes DI a lot more doable, and so on and so forth... Even Doubledoom!
And it's quite good for tricky places with 2 bosses, especially fi they're both fat like in the Slime Pits. If people are having trouble with 2 boss dungeons where they might use LEMISI with poison to reach quite a bit more exploration than they would naturally, it's worth giving it a try and experimenting with it.

Especially if theyre in the "explore everything for bonuses then damage spike the boss" stage of player expirience.