Based on the responses, I'm not seeing any evidence in support of de-tensioning the blades. I would agree that if you're happy with doing it and that de-tensioning on your saw doesn't cause additional issues then it doesn't hurt to do it and errs on the side of caution.

Scientifically, the question comes down to the response of the materials when put under tension in the saw. I assume most if not all spring mechanisms in these saws are made from coiled spring steel which likely are well within their elastic region and likely to have an equivalent infinite life at the stress values seen by the materials. My saw has shown this to be true with no effect on the springs. It comes to mind that we don't know if a manufacturer may have used cheaper materials or have spring designs that are going beyond their elastic properties.

The remaining metal components involved include the wheels, bearings, fasteners and frame components. Once again these are expected to be loaded in their elastic region with an expectation of infinite life. Same argument would apply for a manufacturer using a poor design or incorrect materials - they could fail.

I do think people hear about fatigue failures of springs and such (which can and does happen) but this is a different mechanism and requires repeated cycling. The stress in a bandsaw spring and other tensioned components is a constant while the machine is not in use. When in operation, the bearings, wheels, shafts, and such do have cyclic fatigue effects but this has no impact on de-tensioning while not in use.

The remaining item would be the rubber tires on the wheels. This can vary and these type materials can creep enough to potentially cause an issue. I own a 20 year old Grizzly and while I'm not so confident the materials chosen for my tires were well engineered (maybe I'm not giving them enough credit - I can't say for certain). But even if it is by luck that my rubber tires are of a material that resists creep or taking a set under the loading presented by my saw, the fact is they have done so very effectively.

One other item this relates to is the belts, motors, arbors and other related components on all of my machines are all under tension and also have metal and elastomeric materials. However, I don't nor do I see any designs which utilize de-tensioning each time I leave my shop. Granted they do require replacing under heavy use eventually and once again - maybe I've been lucky but I've never replaced a belt on my equipment either. I am a one man shop that took several years off of woodworking while raising our kids and such. My tools aren't used remotely like an industrial/commercial facility. However, my shop represents quite a nice case study of the long term effect of leaving these items under tension.

My take on this after reviewing this as well as my personal use case is that a well made bandsaw should have no need to be de-tensioned.

I also know that sometimes even a "well engineered" machine can sometimes have unintended flaws that couldn't have been foreseen initially. So the idea of doing it just in case is still valid. Certainly, if you have a saw that exhibited an issue from being tensioned then by all means do what you need to do for it.

It really appears to be riskier to de-tension and possibly start it up this way or to tension it incorrectly. It also seems to like it could add additional wear on components that (at least in my saw's design case) aren't designed for repeated tensioning/de-tensioning.