Well, no caliber lies, .22 or otherwise.
Having a .22 conversion for a defense gun is nifty and can be helpful, but shooting a .22 coversion only has limited uses if you are using it to train with instead of your actual defensive cartridge. You can work on things such as drawing to your first shot, inclusive of things like sight picture and target acquisition. The lack of recoil, especially in regard to followup shots, means it won't simulate your defensive caliber too well. This is a problem noted by some police officers when they trained and qualified with .38 Special, but had to fire their carry ammo in the line of duty, .357 Mag. The flash, bang, and recoil was found to be quite startling. Also, malfunctions don't clear the same way, or often don't.
With that said. for trigger familiarity, fun with plinking, etc., the .22 lr conversions are great.
"If you look through your scope and see your shoe, aim higher."
-- said to me by my 11 year old daughter before going out for hogs 8/13/2011