[dave44]

I'm not quite sure what about this you don't understand, but remember...

"Sklansky's Fundamental Theorem of Poker:
Every time you play a hand differently from the way you would have played it if you could see all your opponents' cards, they gain; and every time you play your hand the same way you would have played it if you could see all their cards, they lose. Conversely, every time opponents play their hands differently from the way they would have if they could see all your cards, you gain; and every time they play their hands the same way they would have played if they could see all your cards, you lose."

Capping more hands means your opponent will have to put you on a wider range of hands and will not be able to play as correctly against you.