Hi i understand how important it is for you to know about the MacScan.
MacScan is an third party developed application which is officially not recommended by Apple Inc or any of its support communities.
Apple Mac operating system is designed in such a way that it doesn't allow any third party application to affect any part
of the data.
As per your question raised let me try to put my answer in a very simplest way so that u would be comfortable to understand.
Ex:when you try to surf/browse/search something in a browser u can see pop ups.ads,banners poping up on your screen
during the search if you are anyone by chance click on any of those pop ups apps are unwanted files start downloading
without the knowledge of the user.
Let me also remind you as u might also know about this google itself allows popups wherein the company's/corporate's pay google for it.
hence you can do an alternate as you have malwarebyte scanner which is not recommended by Apple Inc but the way it works makes things easier searching cached,cookies files manually it is a bit confusing for an user point of view.
Hence use the malware byte scanner to scan things and remove the unwanted files ex:Junk files.
from the device.
Hope this answers your question.
Regards