I'd be extremely chary of using them for VFR flying training (unless you're very young and want to get in some practice before you're allowed up in an aircraft).
But for IFR - it's a different story. I did a lot of hours of IFR, no outside vis, using MSFS and I think that stood me in extremely good stead, both for IMC rating renewals and more recently for the FAA IR. For that, I can't recommend it highly enough. Use the real IFR charts and it's amazing how you can actually fly the procedures (in California and Florida, anyway, which is where I tried MSFS).