You probably accumulate apps on your phone over time, and you likely had a perfectly good reason for installing them at the time. How many of those apps do you actually need, though? The Play Store knows, and it's starting to tell users to ditch those unneeded apps.
Some users are seeing a notification from the Play Store that reminds them to get rid of unused apps. It's a bit reminiscent of the app manager that popped up back in 2016. If you tap the notification, you end up in the Notification section of the Play Store. From there, you can tap again to get a list of apps you haven't used lately. For each app you select, the Play Store shows how much space you've saved.
The notification is far from universal, but that's par for Play Store features. This feature may or may not roll out to everyone, and you might never see it if you keep your phone light on apps.