GPS "almanac" data is valid for a couple of months. So if a GPS receiver is left on long enough to receive an almanac a few days before a trip then it won't be necessary to wait for it in the field. No big deal, but it a ~ 15 minute delay that can be avoided via pre-trip preparations.

A GPS is that is used from time to time probably already had a valid almanac. I was thinking of the more-casual case of one that hasn't been used since the last vacation.

All GPS receivers collect and store almanac and ephemeris data whenever they're on. You don't have to do anything other than leave the receiver on longer enough.