This is what Laguna have to say, if they're not the biggest bandsaw brand in the US then they're certainly one of the biggest,
"Note. If you are not using the bandsaw for extended periods of time (overnight), remove the tension on the blade. This will increase the life of your blade and the machine. If tension is left on the machine, flats or grooves can be formed in the rubber of the wheels, which will detract from the performance of the machine and in extreme cases cause vibration. Removing the tension will greatly enhance the life of the machine, bearings and tires."
Carter Products, who make aftermarket guides, tyres and other bandsaw accessories also advise slackening the tension, I seem to remember as well as safeguarding the tyres and the machine they said some blades can get deformed and stretched if permanently tensioned.
I use a Hammer/Felder bandsaw, they give no specific guidance, but talking to their engineers they say ideally remove tension overnight, but in practise you won't come to much harm if you just slacken off when you're not planning on using the machine for an extended period. I take "extended period" to be a weekend, others may interpret that as a fortnight's holiday or a three month shutdown. At the end of the day we're each responsible for our own output and our own machines!
