When my company first offered the brokerage, I jumped in. It was great with one exception, I was limited to only have 30% in the brokerage side. I did one more large transfer, thinking I could do this every few months. I became fustrated!! My brokerage side was out performing the 401k side due to my choice of investments... My 401k side was getting the automatic investments via payroll, and It was stuck on that side..
Instead of re-investing in the brokerage on a monthly basis I could only due it a couple times a yr. for a few k each time. My 401 k side was my lowest performance funds in my portfolio. I decided due to fund choice to use the 401k as the 'core' holding and the brokerage side for momentum investing.
I wish the entire portfolio could be on the brokerage side. When you transfer treat it as a 1 time event. There are some other advantages, if you are not 100 % vested, but they are not worth explaining here...