More third party developers are starting to add this support to app icons so I'm using it even more outside of my love for app switcher.
Some of my favorites:
Email: I can quickly filter flights or packages, or frankly up to four things that I can edit within the app. Note that in not talking of Apple's mail app, but what I consider a vastly supperior app called "email" by Easilydo inc.
My weather: I can easily check weather in up to four saved locations, one of which is s Ross the world in Hungary so I can either laugh at my relatives or cry at my misfortune lol. Tons of other options here too.
Cartwheel: we shop at target at least twice a week and being able to immediate access the scanner to see if I can save more money on items in already buying is rather convenient. I can also bring up the barcode quickly, however I have that saved as a widget too, slightly faster depending what screen I'm in (generally lock screen at checkout).
Chrome/Safari: incognito/private tab viewing. Some things I just don't want to be in my history or be viewable as open tabs on other devices. This makes loading a private tab super convenient.
Fitbit: recently I've been logging my food intake as I wanted to get back to eating healthy as I let that and working out go a bit on the wayside this last winter. The app was given a facelift (beta) so this useless convenient than it once was (i.e. The app interface isnreallyngood now), but it's still quick access for manually recording. Can also log weight, water, and track an exercise.
Google maps: directions home. Unsure if you can see other saved addresses. Home is all I save because it's the only preset I'll really ever need. Don't use it all that often, but it's a nice and easy way to navigate home without fiddling with a whole lot for when I just can't/won't use Siri to direct over Apple maps.
Damn. That's a much larger list than I expected. I guess that's a good thing.