Do you think Avast waste computer memory much?
On contrary…
Comparing to other antivirus avast is not a bad guy, resource hog.
But, of course, it needs some resources. The best balance between protection and resources consumption is the Normal sensitivity of Standard Shield (and not the High sensitivity) 
avast is relatively light on resources in comparison to other AV (see image). However, if you are having to worry about memory usage, you probably don’t have much of it and increasing your RAM will greatly improve overall system performance. In use the memory requirements will change as it scans files, web pages, emails, etc. so it can fluctuate, but that is true with other AVs.
What is your system specification ?
In the past I have checked memory usage by various AVs, including Avast.
I did not find Avast out of line in that area, and it was much better than some. In fact, I never noticed any slowdown or problem with even the heaviest applications. I would not be concerned about Avast’s memory usage.
Jerry
Isn’t memory there to be used? Whats the point of idling there for nothing when it could be made a good use of it? When you run intensive program it will page that memory to disk anyway…