If I transfer files every few months to the external drive, will I get better external drive longevity by leaving it always on or turn it on for a hour or so every 3 months to transfer my files and then shut it down? I spoke to the sales rep at OWC and she indicated that I should leave it on always. I'm not computer savvy and just want other opinions as it seems counter-intuitive.
If your external drive is a spinning HDD, then it won't make much of a difference. A WD drive lasts years. I'd leave it on - it'll spin for a few seconds once in a while and that's good for the motor.
If it's an SSD drive, then it's better to only use it when required, especially if it is USB powered. But I don't think it'll affect the longevity in any case.
People have different experiences with hard drives - you'll never know whether a drive died when it was supposed
to, or when it was most convenient/inconvenient for you. Hope this helps.