this is one of those theory vs real life scenarios.the mail purpose for sealing a hinge line that has a large gap ie to increase the effectiveness of the deflected control surface.if you have a flutter problem then there are other things to do also.counterbalance the control surface,stiff linkages proper number of hinges.with all the reports of flutter and the widespread use of ca hinges,I wonder if there is a correlation between them and larger than recommended power plants contributing to the problem as it was not a common problem years ago.there were instances of flutter but were easily tracked down to sloppy linkages or improper hinging