why do we need route addition instead of VLAN extension on F5 ?? where we use these type of routes?? like...b route 10.244.7.128/25 { gateway 10.244.4

So can you clarify this a bit better - you have a route to 10.244.7.128/25 via 10.244.48.129.

In this case I assume that the internal servers are based on the 10.244.7.128 subnet. In this case it is feasible to use an intermediate router as long as routing and/or SNAT is in place. However, a better solution would be to extend the server VLAN onto the f5 (possibly via a tagged link) and assign a self-IP on the f5. Obviously you'd still have to consider routing/SNAT but from a network perspective, this should reduce network latency as it will be performed at layer 2 rather than layer 3.

If i've got this wrong then feel free to clarify your question