When a limpdonkey raises, he gives away more information than someone who always raises when he enters a pot. It should be easier to put this guy on a range when he raises than if I raise into you.

This guy has JJ+ AQo+ ATs+... and some of TT AJo KQs. It is a little tricky, because there are different ranges that make up 6%, and different people have different ideas of which hand between KQs and AJo is better.
But if someone with 23/20 stats raises, well there's a lot of suited crap that raises with some frequency and folds the rest of the time. It's much harder to put someone on a range when they're capable of playing 64s many different ways pre flop.

Fish like this, they pretty much raising the top 6% and limp/calling suited connectors, broadway, Ax and 22-99. It's that transparent. The only unknown quantity is what this fish considers to be the top 6%. Maybe he l/c KQs and raises 99, maybe the other way round. But it's much more transparent than a good player's range.