For a low-level character whose base damage is like 2 or 3, even a couple hits of corrosion can double or triple your damage output. Even for mid-level characters with 15-20 damage you're racking up a significant damage boost. Couple with BYSSEPS against a physical-resist opponent and it gets comical.
Heck, last night I defeated the 100% resist troll in the PISORF subdungeon just by smacking him silly with corrosion.
Sad to say it, but corrosion really does need a cap...