For me, I love clipless because I feel more attached to the bike because well...I am attached to it. I like the feeling because to me the bike becomes an extension of my body (sorry, getting weird up here, haha), and that makes me thoroughly enjoy biking so much more. It doesn't matter to me if I'm stopping and going all the time because while I'm riding it's pure bliss.
I have better control over maneuvering the bike, especially in emergency situations. I've bunny hopped over obstacles that have suddenly appeared on the road. I've also been able to shift the bike up to 2 feet to the left temporarily to swerve around an unexpected obstacle and then bring it back underneath be before falling. You can't do either of these with standard platform pedals. Granted these are lower probability events, but if I wasn't clipped in, I would have crashed in all of these situations.
Plus the fact that fallstoclimb brought up, if I don't use clipless, I have to pull up on on a pedal with the top of my shoe that isn't on the ground. It's really a minor quirk and to some (most?) it's not a huge deal at all, but I personally find that more annoying than clipping out.
Clipping out has become so second nature that it's as thoughtless as stepping off the pedal. If your clips are set up properly, then it's not an issue to get in and out. If it's too tight, yeah you can have a problem clipping in or out which can lead to wrecks and/or frustrations, same as being too loose. Also, if they're set up properly it actually helps prevent knee damage because your foot is in the precise position it should be throughout the stroke, not angled left or right, or too far forward or back. If your clips are set up properly, and you're still having knee problems, then likely your seat's too low, or you just have terrible knees and need to pedal lighter.
I don't think clipless pedals are for everyone, but for me as well as many others, it's a huge bonus to bike riding.