Best signs your transmission fluid needs changing

Transmission fluid is something many drivers don’t think about until they face some kind of problem, but I’ve noticed that the condition of the fluid can really affect how the vehicle shifts. I’ve been wondering, what are the best signs that indicate the transmission fluid actually needs changing? I’m not too familiar with the exact symptoms to look out for besides obvious leaks or strange noises. The other day, my car seemed to hesitate a bit shifting gears, and now I’m curious if that could be related to transmission fluid needing attention. For those who have dealt with this, what subtle or not-so-subtle signs help you know when it’s time to get the fluid changed? Do these signs come on suddenly or develop gradually? I’d appreciate any personal experiences or pointers.