My biggest flight sim "side effect" with my private training was the desire to fixate on the instrument panel. MSFS is a great IFR trainer but can't replicate seat of the pants flying or proper sight picture. For example in a steep turn, my initial inclination was to look at the attitude indicator to find 45 degrees and the inclinometer ball to coordinate the turn and not look out the window adequately. With some coaching though I was able to get the 45 degree sight picture of the horizon against the panel and "feel" when I had enough rudder to coordinate the turn, allowing me to better divide my time between looking out the window and making quick glances at the altimeter/DG/VSI. Where flight sim really helped was partly because I did some serious extra geeking out and learned to talk to ATC by flying on the VATSIM network. I ended up with a much better understanding of what ATC can and can't do, the 200 word ICAO pilot/controller vocabulary and was able to comfortably fly in congested/controlled airspace from the beginning, despite learning at an uncontrolled field out in the boonies.
Despite its negative stigma here on JC, past flight sim experience can be a beneficial and valuable tool IF your student is willing to approach their lessons with humility and an open mind. It's unfortunate that it seems to breed so many of these idiots that think they're god's gift to aviation because they have thousands of hours at xyz virtual airline (no doubt letting the autopilot land every coupled ILS approach) but like so many things in life you get what you put into it.
And for what it's worth I soloed at 16 hours, but felt like it should have been sooner.