not really last longer..

some switch on and off every day (same with setting it off when no data received , so HDD stop spinning)

some leave it spinning 24/7 (as main drive during d.loads 24/7) is considered 100% on...

no conclusive data the 1st option will last longer.. maybe some even develop bad sector within their 3year waranty period.. (good thing is can claim) 

of course the main cant be off... but if you have second, can be off...
like mine, the 2nd hdd will off all the time unless need to access the data in the HDD...
performance wise will slow but of course spinning lesser.... good for the HDD also..

what i mean last longer is for those open 24/7.. leave the main HDD on, the rest off