I'll say this in defense of the topic...one of the BTM coaches this month has a column talking about this very thing and how the attitude of "THS is super easy, never change balls" is actually a fallacy.
I take six just about anywhere I go. For tournaments, always seven and sometimes eight (depends on whether I can fit it in with the luggage).
However, that's deceiving. One of the balls is plastic, always gets used. The other five that go to league are all very staggered in regards to layouts, surfaces and intended conditions. And I virtually never use more than two of those.
However, on some nights it could be Nos. 3 and 4 (1 being the strongest, 5 the weakest). Other nights, 4 and 5.
The point is, you have the tools available even if you don't use them. There are nights I've stayed with one the whole night (including the spare ball -- I only use plastic to shoot the 10 and maybe the 6). There are nights where I could have 50 and it wouldn't have mattered.
Changing balls for change's sake is not smart, but neither is being stubborn about switching balls just because you're "not supposed to" on THS. Working under the assumption that we're supposed to be trying to shoot our best score every game, why not use what you've got?
Jess
