With a resident (on-access) scanner the need for on-demand scans is much depreciated. For the most part dormant/inert files are being scanned, the other active files are going to be scanned by the resident shields when they are activated.
There is no requirement to run or schedule on-demand scans. Generally I only run an on-demand scan as a result of a question in the forums.
In fact you probably have the Smart Scan (NOT so smart) set to do a scheduled scan by default, check and disable it if you don't want to run it.
I did run the smart scan, to see what it scanned and or found. Having run it once do you need to run it again, I think not. For me the smart scan seems to be a vehicle to promote other avast paid services.