Well, the story is, I started with one SEP account, then added a Roth. Then fired my broker and moved accounts online.
Wasn't sure exactly what to look for in an online broker, so set up three different brokerages. Added a fourth because I liked having a bricks&mortar brokerage nearby for a margin account with check-writing privileges. Then discovered IB, the fifth one I opened for their tradersworkstation and low commissions, also a margin account, and the one I prefer to trade in.
One advantage is that I can actually make 3 daytrades in 4 of these accounts for a total of 12 per day without getting the pattern daytrader label and without maintaining a $25K minimum balance in any one account -- in my largest account I can trade as much as I like, but it's also the highest commission (but is in an older, and I reckon safer, brokerage house) -- in these times when banks/brokerages may soon be in deep trouble, I prefer to spread "my wealth" around and not concentrate it in one place. One never knows what may happen in the future...
Also, no paperwork problems as 3 of the 5 are IRAs so no tax reporting on individual trades. I keep a daytrade book, so know which account each trade is entered/exited in at a glance.
Hope that answers your question.
Newly