I do it on every cruise just to establish a repoir with the steward. I ask for a little something special as I give him/her the tip..............please make sure room service brings coffee every morning at 8:30 a.m.; will you leave two buckets of ice in the evening? for example. Every cruise except one the steward was very gracious and agreeable.
In my opinion, and it's only an opinion, pre-tipping the steward something, let's them know you are not going to stiff them and set's you apart from the other guests on their list.