What mica said.
I used to have accounts on Ultimate Bet and Absolute Poker. I opened a UB account to play a private freeroll they were hosting for a membership site I used to play on. A couple weeks later, I opened an AP account because they were hosting a private freeroll for the same sight.
Nowadays I don't bother with accounts for different skins on the same network. But I know you usually can't use the same name on different sites on the same network. You can't log onto them at the same time. I know a lot of the skins on the same network offer different rakebacks or deposit/reload bonuses to try to entice users to choose their skin over the others. Except for the private/hosted tournies, it all seems redundant. The rake back might be better at one, but another might have a better loyalty program and another might have a higher deposit bonus.