When the computer loads into the "Safe Mode" version of Windows, many of the drivers and startup programs don't load in the background. As such, if the computer has malware or a virus, then running scans from Safe Mode will frequently allow the program to clean out the junk better than in "normal" Windows.
Under normal circumstances though, running removal tools while in "normal" Windows is the best way to determine if there are any viruses/spyware infecting the computer. Run them as frequently as you think you need to. If you download lots of sites and visit adult sites and such, you might want to scan immediately afterward. If you seldom visit dodgy sites and see nothing abnormal as to your computer performance, run a scan every week or so, may longer. It all depends on your use of the computer.
As to temporarily disabling your antivirus when running SAS or Malwarebytes, it's not required although it tends to let the scanner run a little quicker and prevent any conflicts from arising during the scanning process. It's your choice.
Hope this helps.
i have norton 360 which is on continuously but when i use SAS and Malwarebytes antimalware or ccleaner and even windows defender do i need to turn off norton cos i havent been doing that,also do i need to run these other programmes in safe mode if so why? cos in past i havent ran it in safe mode and now i hope i havent caused any harm to pc! welcome some advice and also tell me if thgese r gd safe gd programmes and how often should i run them!