The money is for the warranty.  SupportAssist keeps working for things like checking for updates and performing diagnostics even without a warranty, but the features related to warranty case creation and tracking won't work without an active warranty.
Does Support Assist really have to be purchased again and again or is someone trying to scam me? I got an email from  saying that I must pay at least $209.57 per year to renew my warranty and keep Support Assist software functioning.  Is there a free alternative to the Support Assist software and why does this link say that there's no charge for the Support Assist software? 
SA, purchase again?