Have a look at: http://www.cisco.com/warp/public/cc/serv/mkt/sup/tsssv/opmsup/stapss/sass_ds.htm for more details on the pros n cons of it. In brief:
Cisco Software Application Support (SAS) includes 24-hour technical assistance from the Cisco Technical Assistance Center (TAC) via telephone and the Web, online tools, plus bug fixes, maintenance, and minor releases* for the software application-all for one annual fee.