Pros and Cons of controlling BPT workflow from interface screen actions

Hi All

Lets say I have a BPT process where I do not specify the Launch On. 


The Approval BPT process only starts when user click on a "Submit" button which will call an action to kick start it.


And when the approval clicks on "Approve" button, it will call an action to close the current BPT activity.


Question

Comparing the above scenario, what are the Pros and Cons of doing in such a way as compared to the normal way of specifying Launch On in the BPT process and Close on in the Activity itself?

One of the Cons is the maintenance.

If you have a trigger and you need to change the trigger, the processes that already started will keep the old trigger and only the new ones will apply the new trigger. The maintenance is a bit harder.

If the entity related to the trigger is used on many places and you want them to interact with that BPT process, then trigger is useful. That's one Pros