Straight consulting... probably not that much, I suppose, but you still need enough to carry you through a couple rough quarters (at least) to retain and serve a steady pipeline of clientele, and be able to account for payment scheduling issues that arise from time-to-time. (Those small disruptions quickly compound.)

I liked having a one-year nest egg stashed away when I was operating at full-steam.

And, of course, smart players will have a little next egg AND have a pipeline partly-filled before leaving a day job. :)