I am interested in determining the differences between distributing sessions via route group/route list vs. single trunk multiple destinations. The assumption is that the destination addresses are identical in reachability and header manipulation. It may be an HA pair or geo-redundant devices.
The only difference I can think of is that with Route Groups you can use circular routing vs. top down which is what you will get with multiple destinations on the same SIP trunk. If the SIP trunk share the same settings of the CUCM SIP trunk and you want top-down routing then it is perfectly fine.
One thing I've seen is having multiple destination addresses ignores the Stop Routing CallManager service parameters. So if you need that to function correctly, you may need to use a Route List with multiple trunks.
You can have up to 16 destinations on the trunk and it chooses one at random. If you want control over order then need to use route groups and lists and add a trunk for each destination.
From Cisco doc,
Multiple Destination IP Addresses per SIP Trunk
A single SIP trunk can be configured with up to 16 destination IP addresses. Unified CM uses random distribution to the configured destination IP addresses when placing calls over a SIP trunk. Using multiple IP addresses on a SIP trunk can help to reduce the need to deploy multiple trunks with route lists and route groups.
