Yeah, that makes perfect sense. Although using an EC while having one link as standby (thus not using that link nor the load-balancing that EC offers) seems quite rare to me these days. I can’t think of many scenarios where this would be used.
A quick question, though. Is it necessary to have just two links in the EC? It’s not a requirement but I suppose that it makes sense to only use it with 2 since the design includes one link forwarding and one link idling.
Yes, I agree with you for the most part. There are other solutions that would probably be better to use for such redundancy. Even setting up an EtherChannel statically would probably be a better choice in many situations. With static EtherChannel, if a physical link fails, the rest of the links will continue to function without disruption. I guess one particular use case is if you have configured a switch to connect to two NICs on a server using LACP. Then using fast switchover is a good idea.
It’s not mandatory in that you can configure an LACP EtherChannel with more than two links and configure fast switchover. However, it is recommended by Cisco that fast switchover be used with only two physical links in the LACP portchannel.