In the latest edition of How to Brew, Palmer tells you to use the stir plate for only the first half of total propagation time (Notes on using a stir plate, p.122). The reason is that the yeast needs some time without oxygen in order to build up it's glycogen and trehalose reserves, which it needs during the lag phase. This also fits with what the guys from Imperial Yeast say in this Beersmith podcast: http://beersmith.com/blog/2017/12/10/imperial-yeast-and-starters-with-owen-lingley-jess-caudill-beersmith-podcast-161/ ,namely that it is detrimental to the yeast if you go on supplying oxygen after the fermentable sugars are consumed. So I do not doubt that this is good advice. It means that if you leave your starter spinning on your stir plate till all the sugar is consumed, you''ll get yeast with depleted energy reserves. That's to be avoided, og course. But I'm not happy about the way the advice is given. It's rather hard to know beforehand what the total propagation time will be. I asked Palmer, and he answered that maybe max 12 hours would be a better way to formulate it, but actually that doesn't help much either. This involves, I think, knowledge about what actually goes on in a starter on a stir plate, and that's not easy to come by. I have some ideas, but nothing I could call sureness. So I'd be very happy if anyone has a link to some good information about that. But what I really, from a practical point of view, need, is a figure: At what SG value should I discontinue the spinning?