The advantage to using MAC addressing even for static IPs is that everything can be controlled from the router itself, rather than configuring multiple machines.
Normally, if you wanted static IP addresses for all your computers, you would have to go to each one of them and assign a static IP in the Network Connections settings.
With Fixed mapping, the router's DHCP server always assigns the same IP address to each computer based on it's MAC address. You don't have to worry about configuring anything on each of the computers - just allow them to obtain IP addresses automatically, and the router takes care of the rest. Anytime you need to change the static IP of any machine, all you need to do is change the IP corresponding to that machine's MAC address in the router settings. Everything is centralized.
Another advantage of this is that it prevents IP conflicts that may occur when you assign the same static IP to two computers accidentally.
But since you say it's not available on the Linksys, you could just manually assign static IPs to each computer individually.