I think that should be of Error's concern but in general, it depends. If you only have one or two rooms in your game where you have realtime floor reflections, you can go away with a cheap trick, but if your game relies on such a feature, you should invest time in it.

If they are done right, reflections can add a subtle degree of "polishness" to your game. It is certainly no great feature which promotes your game, but it is in general a pleasure for your eyes. That is why you wash your hair, add some perfume and put on some nice clothes when you go out on a date - even if you are handsome, this extra polish will make you more attractive to your girl's eyes and other senses. Subtle polish is always attractive - to gamers and the opposite sex as well