Just like .38 Special in a .357...will require more frequent and vigorous cleaning of the chambers. But other than that no consistent problems have been reported that I'm aware of.
The notion that the .40 S&W is a lower pressure version of the 10mm is a bit misleading. It may produce lighter ballistics, but there pressure difference is only 2,500 psi. The .40 S&W is a high intensity handgun cartridge in its own right.
To me, the ability to shoot .40 S&W in a 10mm revolver is a convenience, not necessarily preference. It's nice because there are much more factory defense loads available, and if you don't handload, then practice ammunition is cheaper and much more available.
If you're a handloader, I can't think of really any reason to ever use the .40 cases. You can load to the same ballistics in the 10mm case at lower pressure, making your brass last a LONG time.
Thanks for the detailed answer.
Reason I asked was, I was thinking about the various ".41 frame" size guns such as the Python/Trooper, Smith L, and Ruger GP100. But AFAIK none of these guns have ever been chambered in .41, at least not as a 6-shooter. Is the cylinder maybe not QUITE big enough for 6 .41s? Okay, then, how about .40s? (Smith's 10mm was on the N frame, I believe.) Don't think I've ever heard of any of these guns in 10 or .40.
Now I realize that even if a 10mm will fit, you run the risk of re-inventing the Smith 19 on a larger scale--just a little too much cartridge for long life in the gun. So what about .40s in one, then? (I didn't realize that the pressures were so close.) I'd love to have a gun of this size shooting .40s from snowflake clips. Of course, if you made it, you would HAVE to make it in 10mm "just because" and "why not" but reasonable people will be happy shooting .40s in it, just as we mainly shoot .38s of one sort or another in our .357s MOST of the time.
All just more mental masturbation, I suppose...still, you gotta think about SOMETHING interesting all day at work....