I have always left 401k money with my former employers. (They were large companies). Main reason is the ease of changing investments. I know you are not supposed to time the markets, but I have done so with pretty good results by leaving my funds in the 401k. When I see a potential bear market coming, I go online and transfer, that day, money from the market into the guaranteed fund or whatever option your 401k provider offers that doesn't lose value. So I am earning maybe 3% on that money but when the market tanks, I lose nothing. Then when the market is going to recover, in one day I can move back into some stock funds.
But maybe you can do the same with IRAs as long as they are all in one fund family. As my 401k plans offer 20 to 30 options for investing, I have always had good choices available and just liked the freedom to move money so easily online.