The problem you run into is the possibility of discontiguous network addresses on routers. Routers can handle this if you're using routing protocols that support VLSM. For example, If I have Network A that is 172.16.10.0/24 on f0/0 and Network B 172.16.11.0/24 on Fa0/1.
By default, the Router will be able to do it but not of you have 172.16.10.0/24 on both interfaces. The router will send part of your packets to f0/0 and other parts to f0/1. So you will have packet loss.
Even NAT will not help here. NAT works off of setting your inside and outside interfaces. If you've got 172.16.10.0/24 on both inside interfaces and a single outside interface, it will NAT to both.
Cordially,
Ronnie Wong
Host, ITProTV