I'd hold off on the "No PC should function without these two programs" recommendation for now.
ProcessGuard is a very powerful program. It works at the Kernel Level which means it has higher authority over virtually anything you run on your computer.
All drivers work "at the kernel level". ProcessGuard only has a real shot if it prevents malware from installing; not if that malware is already installed. And the kicker is that the authors of ProcessGuard, DiamondCS, recommend disabling ProcessGuard during software installs. This is ironic, since that's exactly when malware often creeps in.
So, OK, ignore that advice, and keep ProcessGuard enabled while installing software? This can be a recipe for a headache, if ProcessGuard blocks a driver, service, or hook that your new software needs to have installed and working. And the result of blocking it may be a botched install. Usually, you can just re-run the installer, but sometimes you'll have a mess to clean up, or worse.
And the fact that you must
allow some software to install drivers and/or service, or to use system hooks, means that it's a guessing game as to what you can trust. Just try blocking all
drivers, services, and system hooks sometime, and you will quickly see what I mean.
Even if you have a firewall and an antivirus installed and running, there are so many leaks and vulnerabilities that will render those security programs useless. You can see a list of the most common leaktests here: http://www.firewallleaktester.com
My personal firewall software stops all known leak tests. I'm not going to say what it is, because I don't want to engage in a back-and-forth about it.
There are tons of viruses/trojans/worms that will detect which firewall/antivirus software you are using and simply close them down or disable them and then run their malicious coding or connect to the internet. And your Antivirus/firewall can't do anything about it!
Can you name any of them off the top of your head? I can't, though I know they exist. In any case, no malware is going to kill your firewall or anti-malware application if it is recognized and intercepted by the latter. Please don't read into the word "if" in that sentence; I am not saying that security-software-terminating malware isn't a concern, but this is a mitigating factor worthy of note.
Your security software is just going to think you are shutting it down or disabling it.
Only if (1) The malware isn't detected; and (2) Your security software has no self protection features of its own (most decent ones these days do).
To make the long story short, no process guard = no security.
This is a gross misstatement of reality. Security is a direction, not an end point. Shades of grey, not black and white. You're not "secure with ProcessGuard" and "totally insecure without ProcessGuard".
I'll close by pointing out that I (and others) have reported several bugs to DiamondCS that made it easily possible to totally bypass ProcessGuard. I also pointed out a way to kill applications that ProcessGuard was supposedly "protecting". I have no idea if all of those bugs have been fixed, as I grew tired of being their unwitting beta tester.