Sometimes it is nicer/easier/kinder to the front mech' to stay in a range of gears ie on one chainring eg when slogging away up a series of hills.
Surely there's more chance of enabling this by using a double. Less front rings to keep messing about with!!
There will only an extra 2 or 3 gears due to duplication of ratios. I was always told to MTFU!Triple also gives you some nice low gears to boot. Handy if you are not endowed with Oak Tree Trunk Legs, are touring with heavy panniers or trying to shift your bike and your carcass up Wrynose Pass or similar.
Much like the unslammed stem, flat pedals and dork rings the triple is an oft-maligned piece of kit in certain circles. Tis a funny old world to be sure!
Nowt wrong with flats. Wouldn't wear spuds if you paid me!