I rely on these malware tools to prevent/detect the unexpected (just like everyone else) so when there is an option of performing a full scan for everything to detect any intrusions, I prefer to take that route...even if it only eliminates the slightest chance of infection, over a quick scan. In addition, I schedule it to execute off hours so the extended execution time doesn't mater since the PC is not being used. My reference to a 'casual user' is just me indicating that I rely on 'ease of use' with software programs to achieve the maximum protection with as little involvement from me as possible...I want to load it, set it up and forget it. Personally, I understand that users can be satisfied with 99.9% and that's absolutely fine, but in this case, I prefer 100%. I think it's worth running a full scan if it eliminates the .1% change of infection over the quick scan.