Brew a double batch. Split the cake, grow a starter from one half, pitch direct on the other. Ferment and compare?
Honestly, I've done it both ways including (perhaps the third way) of using only a portion of the cake.
If you're ready to ferment the next batch right after you keg or bottle, I see no reason not to go right onto the old cake (or transfer all or a portion of the old cake to a new fermenter).
If you'll be ready a week or so later, save the cake in a santized container and grow up a starter if you want. You can also just pitch the slurry directly at that point, too, as there will be plenty of viable cells.
Too me, it's more about timing and convenience.