This is so useful to me. It allows me to separate my personal life and school life. One time, I showed a Youtube video through Gmail at a meeting. Afterwards, a bunch of anime girls showed up in the recommended tile thing afterwards (it was because I listened to a lot of nightcore at the time, but it was still embarrassing). If you ever worry about something weird showing up on your computer during a presentation, or really any time you have to share your screen, use containers!

It's really helpful for signing into multiple accounts (for example, I have 4 Gmail accounts for school, work, personal means, and an organisation I help run. I don't want to be signed into my organisation's email all the time; I share it with 3 other people, and I'm only temporarily in charge of it. I don't want to have it hanging around, signed in all the time).