Small things are better done right away. They seem insignificant, but they consume your attention and distract you.
It is better to unsubscribe from annoying emails as soon as the email arrives. You're already distracted, so it's okay to spend a few more minutes so that you don't get these emails later.
Disabling notifications in new messengers is also better as soon as you install them. You have spent time to find the application. Another couple of minutes will save time in the future. Just like with routine automation—by setting up a project build system once, you will save time on routine tasks in the future.
Plus, the little things pile up. If you procrastinate, you'll not only need to “unsubscribe from newsletters and turn off notifications”, but rather “take out the trash, do the dishes, turn off notifications, unsubscribe from newsletters and whatever else is out there”.
It's not just a couple of little things. It's a harder and more time-consuming list to get rid of. (Which can lead to procrastination.)
In total, unsubscribe from annoying emails once you get them.