i think you are right . you can see you screen , in the right bottom . if you desable it ,the icon is a "disable" . in that case ,U are in danger . you can disable email scan ,if your hardware is not good (CPU is not good or memory is not good ). i think
Unchecking "Enable On-Access scan at startup" will disable your background scanner so it does not run.. As mentioned by the other poster, it makes your computer vulnerable to downloadable viruses during normal operations.
A "Full system scan" is done by the adjusting the "On Demand/Scheduled Scan" settings.