I have my brokerage business with one particular well-known US brokerage house. I find being able to access my retirement accounts and personal investment accounts through the one interface useful.
However, I was talking with a friend of mine and she said she never puts more than about $50k into any particular brokerage account.
Managing three or four such accounts seems like too much overhead for me. I'd prefer to spend my "investment time" reading up on my investments and researching new ones.
One reason to have more than one brokerage account with different houses is the issue of SIPC insurance:
Within limits, SIPC expedites the return of missing customer property by protecting each customer up to $500,000 for securities and cash (including a $250,000 limit for cash only).
What other reasons could I have to use more than one brokerage account?