I always work in 16-bit mode, so the banding/posterization objection to using ProPhoto does not apply. You should do all your edits in 16-bit mode, regardless of your choice of color space.
The objections related to ProPhoto being larger than monitor gamut aren't particularly valid, either. Like printers, monitors are improving, so this year's out-of-gamut color may not be next year. If you have some out-of-monitor-gamut colors in an image, it's better to have a color space that can contain them without clipping. Say you have a image if a brightly-colored flower that has some colors that fall outside your monitor gamut and Adobe RGB, but within ProPhoto. If you edit in ProPhoto, even if the flower appears to be a clipped solid color on-screen, if you desaturate to bring the colors into the monitor gamut, you'll be able to see detail that was there all along that the monitor couldn't display. But if you use a smaller color space for editing, those colors will be clipped, and nothing you can do will get them back. You'll have an area of solid, detail-free color in your image. I really don't care if I can't see a color or not; if I can avoid clipping it by using ProPhoto, I at least have some real data to work with that I can edit to bring in-gamut if I need to.
As to the "precision of control" argument, can anyone give an example of a Photoshop tool that has unacceptably imprecise adjustments when editing in ProPhoto?