By stopping the (a) system tray icon twirling would that help with using less system resources?
Anyone have any valid reasons for not doing this?
I have my Avast sensitivity settings set to high by the way.
A very very few resources… but indeed, it will.
The High level is not the best balance between protection and performance.
If you want this, try Normal level.
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the animated icon would be virtually zero resources use as it is a part of the ashDisp.exe and that is very low in resource use anyway.
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a) the rotation of the icon may be your first indication that there is something going on on your system, e.g. avast is scanning. b) it wouldn’t achieve your aim of reducing resource use.
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there is your answer as far as any concern you have about resources, stick with Normal (default) is more than adequate as far as a balance between protection and performance is concerned.
I have set all installed providers to normal setting.
Is there any that I should set to high?
I don’t think so 
Ok, thank you Tech.
What actual difference occurs between the normal and high setting?
On help file, there is info about each provider. In some of them there are no difference between Normal and High, the buttons are there just to make the interface identical for all providers.
Sorry but, do these settings affect the actual program manual scan, or are they for more real time scanning or both?
Your problem is one of not having a high performance system nor OS, so you have to balance what you have and the impact increasing sensitivity might have on performance. Only you can determine if the performance hit is acceptable and you can only do that by trying it.
I have the Internet Mail and Web Shield set to High without any effect on my system. The Internet Mail shouldn’t have much of a performance hit as it is only during email scanning, which won’t be that frequent. The Web Shield might be a different ball game as you will be using that much more and may have an effect on performance.