In my opinion it all depends on what you want to do. You could harvest one cake, then make several starters from it, so long as you go through it relatively quickly. But I just harvest and repitch, harvest and repitch. I think I can do that about 20 times with my system and sanitation without ill effects. But I usually repitch about 4 times, get bored and change styles. Though I've really fallen in love with my 1728 and 2112 so they may stick around.
I have been running 1728 in a mild and an IPA. I repitch the mild to both and toss the IPA. Keeps the dry hop pellets out of the next batch.
I think my methods are sound for my way. I'm certain it could be far more technical. I'm just avoiding gross deviations from good basic yeast handling. I use fresh yeast, not overpitched, not underpitched. But I'm not OCD about it either.