Routerboard throughput comparison
IMHO, no reason to disable it.
Both rb133 & rb532 show 55-70% increase in speed. The rb4xx, rb600 & rb1000 routerboards should have enough CPU to keep connection tracking enabled while also maxing out 100mbit Fast Ethernet ports.
But keep it enabled if you are using Queues, Equal cost multipath routing
or anything else that requires Connection Tracking to work.
I replaced a rb150 router with a rb450 router recently because I needed more speed & throughput but couldn't disable connection tracking due to the requirement of multipath routing & queues.