The tiller is slightly different for 3-under and split--I think the difference is generally around 1/8". Shooting 3-under does put a little more pressure on the bottom limb, but the difference isn't generally enough to affect on the way the bow shoots. One bowyer I know had a pro shooter do some testing--he shot the same bow tillered for split, 3-under, and even with a negative tiller (tillered upside-down for 3-under--I guess you could say it was tillered for 3-over). They found no difference in accuracy. The main, and pretty much only, difference they found was the bow can be a little louder if it's tillered for split and shot 3-under, and vice-versa. This doesn't always happen--it can vary depending on the bow, the shooter, etc.

G. Fred's example is misleading, I think. In his video he has a super light-weight bow and "proves" how out of balance shooting 3-under makes the bow. The example he gives is exaggerated and extreme, and in my opinion not accurate--if it was anywhere near as bad as he makes it look, nobody would be able to hit the broad side of a barn shooting 3-under. He also neglected to mention that bowyers can and do adjust the tiller for 3-under to remedy the problem he highlighted.

You can get a lot of good information from experienced shooters, but keep in mind that we are all human, all liable to be wrong at one time or another (regardless of experience), and what works best for one shooter may not be best for another.

Chad