While it's true that it's currently at 0.5%, what you wrote could be understood as meaning that it changed today.
The maximum profit per roll has only changed twice, as follows:
2013-06-20 started at 1%
2013-09-25 10:34:16 changed to 0.25%
2013-09-28 00:00:05 changed to 0.5%
To the best of knowledge, the only real reason to play under different names is so that the casino isn't spooked and lowers the maximum bet. Other than that, I can't see any real advantage.
Some reasons I can think of:
Gamblers are superstitious. If you stay on an account too long, maybe you wear out its luck. Maybe you don't quite trust the site operator, and think he could be turning on the imaginary doomswitch on your old account, so you make a new one. Maybe you have built up a reputation as a whale who never loses, so you make a new account each time you play, and if you lose you pretend it wasn't you. If you win you can shout "yes! I won again!" - but if you use the same account all the time the site owner will easily be able to make a chart of your wins *and* losses and people will see that sometimes you lose.
Statistically you would eventually make the money back, but you still have to meet the loans by investors.
Borrowing money to gamble with, even when you're gambling with a positive expectation, seems dangerous. The people lending coins to Just-Dice are fully aware that they might not get as much back as they lend, and are happy with that deal.