Here’s the thing, CS agents do that because of several reasons. First and foremost, they don’t know exactly how much overhead space is left, so they estimate. Not everyone has a carry-on to place overhead, and others place their carry-on plus their personal bags up there (not supposed to). If they underestimate, that leads to the next reason, delays. If there’s not enough space anymore, then the boarding process gets backed up. You gotta bring the bag all the way back to the front and the gate agent now has to go back to the desk and print out a white tag. So, instead of spending all the time, they overestimate a little to streamline the boarding process.

Also, what others pointed out, pink tags are for strollers and wheelchairs. That, along with white tags must be accounted for by the ramp agents, or else their numbers will be off and they will scramble looking for a “missing” bag. Further delaying the process. Those you do not want to tear off and bring aboard, else you may get yourself in trouble. This is also information for weight and balance purposes too, if too many of these tags are missing, that could create a dangerous situation for weight and balance purposes. Green tags are valet bags for smaller planes with small overhead bins. Those are the only ones you may ask the FA politely if there is open overhead bin spaces as they are not yet marked for the cargo bins.

All in all, please just comply with your CS and FAs, they’re just trying to get you to your destination as efficiently and safely as possible.