I know that method. Kinda like "spot torquing". Tighten it until you see spots.

 

"Don't leave a load on springs" is the common wisdom for most things (I don't know about torque wrenches exactly). But in the gun world we have found that compressing and decompressing springs does more harm than compressing them and leaving them compressed (guys who load and unload their pistols magazines daily wear them out faster than guys who leave them loaded), so it might not be that big of a deal.

 

If metal is not deflected beyond its specific yield strength repeatedly compressing and decompressing does no harm. The question is; was the device designed to operate very close to (or even slightly over) yield strength (which would result in a finite compression/decompression lifespan), or is some other mechanism, such as actual mechanical surface wear involved. As for gun magazines, many of the problems associated with heavy repeated use aren't related to spring damage but rather feed ramp and magazine housing wear.