We go up to 7 generations before starting a propagation. With the idea we can keep going to 8-9 generations should something go wrong with the prop.
Too much yeast? You'll lose some esters and phenols but its a trade off to a good fermentation.
Pros pitch more yeast then the average home brewer for many reasons. Big ones are below.
1.Fast fermentations. time is money. 7 days from heat-x to bottle means quick turn around of equipment.
2. We don't free temp ferment. We ferment on the cool side of things, mid 60s. Makes for a cleaner beer but ale yeast gets touchy at those temps. More is better. As where a homebrewer free fermenting with 6x10E6/ml would be fine we might not finish out.
For almost any beer, ale or lager, we pitch a million cells per ml per degree Plato. So a pale ale of 13degP gets 1.3x10E7/ml cells. You'd need a microscope and a hemacytometer to do cell counts.