Well, that goes to several schools of thought. First of all, yes, it will help cure some flutter issues, but the point of closing the hinge gap is to prevent "bleeding" of air through the gap and reducing the effectiveness of the control surface.

This is most noticeable on larger models, or models that do serious aerobatics, or with experienced pilots that can notice those subtle changes.

For trainers, and new student pilots, well, the gap issue is just not enough of an issue to be a problem. Most, if not all, student flyers are so focused on flying the plane, they never will realize the differences sealing the gaps will give because they don't, for the most part, realize that that difference may be. In other words, everything the plane does would be considered, by the student, to be part of the control and the subtle causes by the gap will never be noticed.

This is an opinion, of course. I'm sure there are different opinions and most will be offered.

CGr.