What's the point of Software Assurance on a MS Volume License?

Question

I'm currently trying to buy a whole bunch of Windows 7 licenses to upgrade XP and Vista Home Premium to Windows 7 Professional.

It seems like a good time to start on an Open License agreement. Every time I talk to a vendor, or go through Microsoft's Licensing website, I see references to Software Assurance.

Apparently it offers some level of updates.. I'm confused though. I thought updates were already free for anyone with a genuine copy of windows.

• Do you have a license with Software Assurance enabled?
• What do you use the "Assurance" for?
• Is it worth the extra £90ish?

Answer 1

Software Assurance provides access to the new major versions of the software; for instance, a Windows Vista Software Assurance customer got automatic access to Windows 7 when it came out, for no additional cost above the Software Assurance.

Basically, it's buying the software on subscription instead of paying the upgrade costs all at once when moving to a new version.