If you already have a TIRA that includes some post tax money, think twice about moving your 401k to a rollover IRA. If later you decide to do some Roth conversions, your post tax dollars (non taxable during the conversion) will be diluted by the pre-tax dollars in the rollover account.
Generally, in deciding whether to move 401k money to a rollover IRA, you must compare the 401k you're in with the most favorable (to you) IRA provider you can find. In my case, I'm doing some Roth conversions (as above) and my former employer's 401k is excellent (a excellent web site and customer service plus a small selection of extremely low ER index funds - yes, lower ER than Vanguard!), so for now I'm sticking with the 401k.
Do you already have TIRA(s) with some provider? Are you planning on doing Roth conversions? Are the few unique protections that 401k's have that IRA's don't important to you? How do the features/costs of your employer's 401k compare to the features/costs of the best IRA provider you've been able to find? There's your answer as to whether to move or not.
I've been retired for 7.5 yrs and I'm about one third IRA and two thirds 401k. DW, OTOH, had a 403b with crappy features and costs. She's been retired 12 years and is 100% IRA. She did a rollover immediately upon retirement (couldn't do it fast enough) because the costs were ugly. YMMV