"start work" button on activities

Hi again!
As far as I can see, the "start work" button for real time working is available on tickets only.
Is there any particular reason to not make it available for activities also?
I understand that since activities can be planned and put in relationship each other, this can make them difficult to manage in terms of "real time" timesheet because of stating a time propagation rule. I mean: some activity types could not require to have time input or not being present in the timesheet for a validation. Nevertheless it could be nice to have the start work button so the time sheet is automatically inputed. The rule could be linked to the activities type field named "can have sub-activities". If unchecked, then it could be possible to have the "start work" button (or input timesheet manually. CRUD operations are anyway permitted from the timesheet screen). The timesheet could be propagated to the parents activities just like now. In this way a resource can work on the task and the time will be automatically registered until he/she clicks again on the "stop work".
Maybe all this already exists and I did not realize it...
Have a nice day!