I have never done it, but I have seen people replace their tone control with a varitone. It makes a certain amount of sense to me to have preset tone settings that you like so you don't have to fiddle around trying to get them with a pot. Keeps things simple and quick to set.

Some years ago I modded the tone circuit on my G&L bass to get just about every passive pickup tone that it was able to produce. In the end it had 4 pots, 3 three-way switches and 4 two way switches. In my garage by myself this gives me a lot of options. But live it takes too long to get things dialed in, so I generally just set it one way and then only adjust the volume. It's how I came to see the value of simple, intuitive controls.