All-in-one security suites offer an array of advantages versus best-of-breed.
As a security professional, you want the best. All else being equal, why wouldn't you want the leading antivirus protection, perimeter firewall and antispam filtering? Your computer and network resources deserve nothing less and it will help you sleep better.
The problem is that all else is not equal. For some companies, a suite of security products from a single vendor is a home run and offers many advantages over implementing separate, best-of-breed products from different vendors.