Incandescent bulbs make things easy. Because they work by making a material hot, even if you feed them with 50 Hz AC power, they’ll stay mostly lit. The first set of LED Christmas lights, however, were massive eyesores for a lot of people.
Flicker fusion
There’s a few important things to understand about yourself.
The flicker fusion speed of the eye is somewhere around 50 Hz. But it’s personal, so some people have an easier time than others with frequencies.
However, if there’s motion, you can see a 50-60 Hz light flicker as it crosses your viewpoint and it can be very distracting.
And, as it turns out, if your flicker fusion is just a little more sensitive than others, for whatever reason, maybe traditional Christmas lights give you a headache and the older LED taillights make you want to rear-end people.
You most certainly care about the PWM speed for LEDs at least a little bit, because you want something that’s at least a bit higher.
Acoustic hum
There’s another thing to consider, however. 60 Hz is a hum you can hear. Your hearing goes all of the way up to 20 kHz or so. And some of the parts inside of your average piece of electronics, like the capacitors, will hum just a little bit. This is a huge problem if you are running a recording studio or something but maybe otherwise you just notice this little humming noise.
Photography and videography
I care even more about PWM speeds.
I photograph circuses and if the stage lights are PWMing at even at 1 kHz, it’s going to create problems for photography and video. See, as a photographer, you might want to set the shutter speed to 1/250th to freeze the motion of a performer. If you are a videographer, you are going to also potentially want to have the shot be crisper so while you are shooting at 30 or 60 Hz, the shutter speed (or, from the days of film “Shutter Angle”) might be set similarly fast.
A lot of cameras end up having a progressive readout on the sensor, either because that’s the only way to do it, with respect to video, or because the mechanical shutter is noisy and shakes the camera and so it’s otherwise better to dispense with a mechanical shutter.
If you are PWMing at 1 kHz, this means that a 1/250th shutter speed is going to capture 4 discrete strobes, which can lead to banding.
Plus, as I said, that’s a 1 kHz hum, which is really far into your hearing range.
Tl;dr:
All things being equal, what you really want is to PWM at a frequency higher than hearing range.
Except that most switching power supplies for LEDs are designed to be PWMed at 500 Hz to 1 kHz. And MOSFETs are easier to drive at that rate instead of 20 kHz.
So a lot of stuff is at 1 kHz, which is a lot easier overall and kinda good but it still drives me up the wall.