My wife and I play a lot together, consequently we check our tuning every time when we start out to play. But when playing by myself, I'll only clip on the tuner if something sounds off -- and it usually doesn't (unless I'm breaking in some new strings).
I have ukes with preamps I added or that came with one, which have built in tuners. I have no ability at all to tune by ear, even after playing guitar for almost 50 years. I totally rely on a digital tuner attached to my ukes.
8 tenor cutaway ukes, 5 acoustic bass ukes, 10 solid body bass ukes, 7 mini electric bass guitars
When I put new strings on I tune it after every song that I play. With that approach, I find that it stretches and settles the strings much faster. Once the strings are settled, I'll usually check the tuning before a long playing session but I more often than not find that it doesn't need tuning. If it's going to be a short playing session I won't tune it or check it if it sounds OK.
Whenever I think it needs it, which I guess equates to every fifth or so time I pick it up (once new strings are bedded in). The intonation on one of my ukes is so bad, it's hardly worth tuning it ever!
Yep. Sometimes the temp & humidity changes will cause me to adjust the tuning several times during a club meeting. On strings that had been stable for a week and only needed tuning when I first picked a ukulele to play.