To kill fast run (which has to be done in site admin prior to working in the project): Go to the Siteadmin > select your project and expands its tables > go to DATACONST table and run below query (enlist your DBA's assistance if needed):
INSERT INTO DATACONST VALUES ('AUTORUN', 'N')
This parameter will remove the ability to do fast runs for this one project.
As inquired about side effects, there is one negation and one slight learning curve.
Let go over the learning curve first. How this is works if you try to change status from execution grid of test lab, the status will let you pick a different status (say no run to passed). And this new status will be in the grid. As soon as a user though clicks away to something else, the status will revert back. No run is actually created. The click away refresh's the non change back to what it was. This can confuse a user if they thought they did create a fast run though. They might not notice it.
Workarounds to avoid confusion would be to instruct all users that fast run is disabled and any attempt won't save or create a run. Or could add in some workflow to add in a message box to pop up and let a user know at a status change attempt that such is a no go.
Example code to give a message box and to do an auto refresh on the field (instead of waiting on a click away to have the status refresh back to what it was originally).
On Error Resume Next
If Fieldname = ''TC_STATUS'' then
msgbox ''Fast Runs are disabled''
On Error GoTo 0
The one negative I mentioned above concerns N/A. Seems with fast run disabled, N/A is no longer a choice you can make. If you pick it during a run, seem it just goes to ''not completed'' for status. N/A does not seem to ever hold as you can only pick it during an active run so I guess that nullifies N/A.
Workaround here is just add a new item to the default status list. NA or something similar. This can be chosen as a status per step in manual runner. And it will write to status when you stop the test. Would just need to instruct your users not to try to use N/A anymore. As its a system list default value, you cannot delete or edit the existing value. But you can add new items to the list. That is best workaround for N/A concerns.