a lot of cameras to this day drift their TC after jamming, unless you ride the clock-it on the camera.
the TC slate is usually more reliable to run in sync with the audio mixer's gear.
you can actually playback the camera, and see if the camera's TC on the recorded clip is off. so you can fix drifting issues as they happen (so you will get a less angry email from the editors tomorrow).
same reason if you jump back and forth between offspeed and project speed. cameras may not keep internal TC correctly.
continuity likes to see TC on the slate for various reasons, especially when video village monitoring is set to 'clean' video (just the frame, without all the camera info junk)
ADs like to keep score of first shot of the day/after lunch/etc.
more informally, slate TC is often used by ADs to see what time it is if they need to dig into overtime or ask for a few more minutes to finish a shot
Edited by Kyryll Sobolev, 06 September 2017 - 12:34 PM.