Effectively my opinions are in my settings in the images I wouldn’t select them or deselect settings if I didn’t think the action was in my best interest.
If you haven’t got auto update of VPS set and a manual check/update before the on demand scan. It may not have the latest definitions, potentially making the scan less useful.
Generally I have only run an on-demand scan as a result a question in the forums (very infrequent). Yet here I am after over 20 years of using avast and no infections - lucky I guess 
EDIT: From memory I set the first, but I think those two settings aren’t of much direct use to me, why they probably aren’t enabled on my settings.