Also nice is the in-service rollover, so you can roll funds directly from the company's 401(k) plan into your self-directed IRA or whatever multiple times per year, instead of when you leave.
Good point. Another nice option is the ability to roll over an existing roll over IRA into a 401(k) -- not all plans have this option. This is important because having basis in an IRA negates a lot of the advantage of doing a backdoor Roth IRA, but if you can move all of those IRA funds into your 401(k) without any tax consequences, then you're golden.
Note that 401(k)-to-401(k) rollovers are generally always allowed.
