HSA gives you hardware redundancy within the system itself. Use of the Hot Standby Routing Protocol (HSRP) can assure highly available connectivity between hosts and routers. Redundancy within a system is useful, but addresses only a small percentage of the failures that result in network outages. Most failures occur on links---especially WAN links, and such failures are handled by the adaptive rerouting mechanisms in the Cisco IOS software which assure highly available connectivity within a routed network.
So, even if you are using HSA on your 7513, it is definitely recommended that you use HSRP if your network layout permits you to.
Also, with HSA when the master fails, the slave reboot the router and that will take time to reload the whole router. With HSRP fallback to secondary router is fairly fast, about 10-30 seconds, considering switching layer convergence.
