Backing up the data on your iPhone is obviously a good habit, hopefully one that people got into back in the days of iTunes synching. Back then if you lost your iPhone and weren't regularly backing it up on iTunes, you stood to lose a lot of data, including photos and text messages among other things. iCloud has made data backup a simple process that happens in the background without any effort on the user's part other than turning it on in Settings. Third party apps can be backed up in iCloud as well, including WhatsApp.
Apple wants its TV app to be your home base for all of your video streaming services, and while it has yet to integrate with Netflix or Prime Video, it has done a decent job collecting smaller subscription services into one place. With the latest iOS update (13.4) it has added settings to let you control how much bandwidth it uses if and when it uses your cellular connection.
Organizing your photos into albums can be a lengthy, painstaking process, especially if you have thousands upon thousands of photos to sort through. Fortunately, the Photos app for Mac has a tool that can be useful for this task - Smart Albums. Basically this tool lets you automatically group your photos by a number of criteria into albums. Unfortunately, and for unknown reasons, smart albums don't synch with iCloud, so you won't be able to create a smart album on your Mac and then view it on your iPhone.
iOS 13 introduced iCloud folder sharing (and it finally came to full fruition in iOS 13.4), allowing iPhone and iPad users to share folders (instead of just files) with each other via iCloud Drive, giving it a Dropbox-like usability. The same functionality came to Mac with macOS Catalina - here's how to share folders from you Mac with other iCloud users:
There are plenty of situations where a different phone number can come in handy - basically any time you don't want to give out any personal information, which can link to other private information and so on. Perhaps you want to sign up for a service that requires you to verify by texting you a code (which just about everything does) and you don't want to give out your real number; maybe you need to text with a stranger who wants to buy something from you on Craigslist; maybe you want to use a different number for a Tinder date.