I've read that you can leave an ale to secondary for months and enough yeast will remain in suspension that you won't need to pitch additional yeast when bottling. But are there times when you do need to pitch more yeast before bottling to ensure you get carbonated beer? For instance...
What if you crash-cool your ale? Will the yeast fall out of suspension such that there won't be any left to carbonate your brew in the bottle?
What if you started with a high gravity beer and the yeast gave all they had? Will they be too tired to eat the priming sugar?
Are there any other factors that would make it a good idea to pitch more yeast before bottling?