While many people buy a coffer and use a standard disposable cup, many others keep their own stainless steel cup and use it in their cars. If the car's cup holders don't have a grip, then the stainless steel drink holders rattle during the drive.
This seems like a small issue, but it can be annoying when something keeps rattling in inside the interior during the ride.
Therefore, it would be really nice if Tesla designers could design Model 3's cup holders in such a way so that stainless steel cups or stainless steel drink holders don't rattle during the drive.
Ford Fusion has done a good job in this regard and it's something even other car manufacturers should look into.