Difference between route based vpn and policy based vpn

Security ASA
1

Hi, I want to understand the difference between route based vpn and policy based vpn with respect to how it is different for the same set-up? For eg. If I have two sites (A and B) and each sites have subnets (X and Y). The Goal is send the traffic encrypted between these two subnets, but how the route based or policy based makes the difference here?

And what advantages will I get in using one over the other in the above set-up

               ┌────────┐                        ┌────────┐
               │site A  │         Internet       │site B  │
 Subnet X──────┤        ├────────────────────────┤        ├───────Subnet Y
               └────────┘                        └────────┘

Thanks in advance!