every event you place under the group will not start when its deactivated. I believe it will end certain loops.
Also, i use multiple groupsiie, user controls, enemy spawn, layout start, menus.
when applied correctly, you can disable lots of functionality when you are at a certain view ..
At first I did lots of "when visible" things, but that takes lots of work and lots of places to update things when something needs changing.
With the groups however, you can move stuff in lots of groups, and groups of sub groups. you can even stuff groups in loops as part of a while or for loop, and have parts of the loop as a conditional factor.
Not only will it help in limiting user input or disbling game activity, it also forms your code in a nice overview :)