I sometimes add more yeast at bottling time. I'll pick a highly flocculant dry yeast like Nottingham or S-04. I've already taken the time to let the beer clarify, so I don't want to add yeast that is going to stay in suspension. I rehydrate the yeast according to the manufacturer's directions, add my priming syrup and rehydrated slurry to the bottling bucket as I'm siphoning to let it mix well, then I bottle. 3 weeks later its perfectly carbonated and ready to drink. I haven't seen dry yeast manufactures recommend anywhere using a stir plate for any number of days, but I may not be looking in the right places.
People will preach that time heals all and that you don't need to add more yeast. That works too, but when I have an imperial IPA that's gone from above 1.080 to 1.008 and has been dry hopped with lots of expensive hops, I don't want to be waiting months for that tired yeast from primary to get things carbonated. I'll loose too much of that fresh dry hopped character I'm going after. For a Belgian triple or imperial stout that benefit from long term conditioning, I may skip that extra yeast addition at bottling. Same thing with average gravity beers. They have all carbonated fine without extra yeast. But, I have noticed that my high OG/high ABV beers take significantly longer to carbonate without that extra yeast addition. They eventually do carbonate though.