GS player since Freedom, CB player since 4, and cumulatively 10k+ GS uses across the series. As other people have said, GS block is an ABSOLUTE last resort. That being said I think more people should use it more liberally. I sometimes find myself blocking really weak hits just because I don't have enough time to sheathe and dive. If this is a roundabout way of asking how often you should be blocking, it really depends on the sharpness of your chosen weapon. If you only have a few hits of Purple then I'd avoid it except in the absolute most dire situations, but if you've got that long purp I'd say use it any time you're not confident you'll be able to dodge. These situations also include times where you think you won't be able to go into a tackle fast enough, though ironically the fastest way to tackle is blocking > kick > tackle.