What's the use of these activity things?

[Shabakthanai]

If you unlock widgets and right-click on the three colored dots on the panel, usually it gives the option to remove the widget. By removing the widget you ostensibly remove Activities. At least that worked for me. I hope I understood your desire.

[Silent Observer]

Unlocking widgets still doesn't seem to offer an option to remove the activities entries in the cashew menus. I could (and long since have) remove the activities icon from the main panel, but that doesn't disable activities, just makes it a little harder to switch activities accidentally.