route rule vs mangle pre-routing

hi.
i manage a network which has three gateways and 4 lan subnets.
i am using mangle pre-routing for routing traffics separately. and adding default route rules with mark-routing option.
in my senario i have to add accept action in mangle before pre-route rule for routing local traffics between lans.
i findout /ip route rule can mark route table same as mangle.
what is the exact differances between mangle and /ip route rule?
which one has lower overhead on cpu?
what is the benefit of using route rules?

Good questions…
Source NAT is to tell the router how to handle private(local) IP to public IP translation and back BUT
this does not tell the router how to route the packets. So it is the admins job to get the packets to the right interface so that the sourcenatting can be done.
At least that is my infantile interpretation.

Mangling is a way to mark traffic such that the marks can be used in rules and primarily from what I have seen is in routing rules to ensure the applicable traffic is sent via the right routing rule.