I have used Spyware Blaster for many, many years. It likely hasn't done much, but it causes no problems, and doesn't use any resources. I also have ExploitShield running for a few weeks. It too does it's job silently, and no drag on resources. I have way overkill protection, but none of it drags my system down.
I have avast! free as my active AV. I have Aviria Antivir installed with the active guard off, as an on demand scanner. I have Malwarebytes Pro, and SAS Pro I won in giveaways. I also have Emsisoft (formally A Squared) as an on demand scanner. Spyware Blaster and ExploitShield. Keyscrambler and Zemana Antilogger. All won in contests or from giveaways. All play nice together, and I have never had a virus since I have been on PCs. Oh and Comodo Firewall with Defense+ on.
I also make weekly complete backups with Acronis TI (2), and Paragon Drive Backup Professional.
Nothing is getting on my system, and if it should, I will have a clean image back in 15 minutes
If all this protection caused any issues, or slowed my system down, I would go leaner, but the multiple levels of protection are great peace of mind.