Support.
I only follow small amount of people that I'm actually interested in. Most of them do the same. “What's happening” is used by us a lot. Having just 5 latest activity makes it easy to miss when someone releases a project. “Projects by Scratchers I'm Following” section on front page broke after website updated to scratch 3 and to this day remains broken. Even if it got fixed, it is still not possible to find out about project being shared as soon as possible.

The bigger reason why I support this suggestion, is the same one why many people say “no support” in this topic. Implementing it can force more people to use followers feature in the intended way.

Currently too many people use following feature incorrectly, by pressing follow button just to make the number go up because it has almost no consequenses and they assume that the bigger number of followers makes the person who has it happier. As a result that person ends up with a lot of active “followers” who absolutely do not care about what that person does. To me putting something to actively discourage misuse of a follow button sound like a great idea.

Some people say that they are going to have their inbox spammed. To those people I can say:
If you are interested in those projectes than why is it a problem?
If you are not interested in those projects than why are you following those people? Following - is not a fame counter, and should not be used as such and as a way to show respect to someone. Following was designed for the purpose of seeing what someone else is doing.

Problems with this suggestion:
1.People could accidentally share something they wanted to keep unshared
2.Someone could purposfully cause spam
3.Private chatting by sharing and unsharing projects with a specific names
4.Inactive users are going to have their messages flooded

Solution:
Instead of notifying something like this:

SpammyScracher shared Untitled-5
SpammyScracher shared Untitled-4
SpammyScracher shared Untitled-1
SpammyScracher shared Untitled-3 copy copy
SpammyScracher shared Untitled-3 copy
SpammyScracher shared Untitled-3
SpammyScracher shared Untitled-2
SpammyScracher shared Untitled-1

Notify like this:

SpammyScracher shared 8 new projects since the last time you checked your messages

I know! Maybe there should be a bell that appears next to the follow button! And when it's turned on, It will say “You will now be notified when (User) shares a project” and turning it off will say “You will no longer be notified when (User) shares a project”

support since in the activity you could miss it if you dont log on. or maybe they should make it so that you can scroll to the beginning of time in the what ive been doing section.