Most people are tethered to their smartphone. It's never more than a few feet away and it's used for everything. It's a stereo, megaphone, connection to the world, to the internet, to friends and family. It's a way to bank, to get directions, to remind yourself to drink water, and... it can be something else... oh, sometimes it's a telephone.
You need to know how to get the most out of the device you use most. Having a few tricks up your sleeve is necessary. If you're going to use it for everything you can think of, it's worth knowing some clever workarounds when things aren't working quite right.
Mr. Hacker's video of 10 hacks for your smartphone has a few well-known essentials in there — using a glass as a speaker, making a hanging pocket for an electrical outlet — and a few you might not have seen before that are useful, like using a drop of water as a camera lens.