24, 48 or 72?

Take a look at your deodorant.  Mine says it's good for 48 hours.  48 hours?  I take a shower at least once a day, so why would I need a deodorant that lasts longer than that?  And now I find that stores offer some that last 72 hours.  Does that mean I could forego washing under my arms for three days?  Well, it ain't gonna happen - I'm buying the 24-hour stuff next time we shop.  Sure makes one wonder, though.