I suppose they do. Especially on these boards, where mountains are made of molehills and bones vulture-picked on a regular basis. But, I know that professional customizers frequently recommend adding mass to the head/tip to slow down a swing. This is often recommended for juniors that are swinging out of control. Adding weight anywhere in the head will raise the swingweight. Raising swingweight, according to nearly everyone who's swung a racquet and cares about such things, and the only studies that have been done on racquet specs and swingspeed, will slow down the swing. However, there's also the line of thought that players with grooved strokes will swing any racquet at pretty much the same speed. From there you could conclude that a heavier stick is better, as you'll swing it the same speed anyway, so why not swing a heavier and more stable stick. I've also seen comments about lead at the tip helping the frame "come around" quicker, like it's picked up momentum earlier in the swing and is now carrying that momentum into contact. There might be something to that. A physicist could probably tell you, but then he'd likely be hectored off the boards by people lacking curiosity. The thing is, most of what we know about the interaction of racquets and players is anecdotal, speculative or theoretical. There isn't much experimental science behind it, so all statements should ideally be made in non-dogmatical terms. But most of us aren't in the habit of qualifying our speech or writing. In my opinion, that's why we end up with train-wreck threads, like this one.