I want to touch on BGP peer groups in this tidbit to explain what they are & why they are important.
Peer groups in BGP can greatly simplify configuration when BGP neighbors share a lot of the same outbound policies. What I mean by this is, if you have several neighbors who all share the same policies, your configuration can & will be much shorter if you use a peer group. This is because you no longer need to specify & configure each individual neighbor with the same policies. Note that one important catch is that a peer group must be either all iBGP or eBGP members. Peer groups also aide in saving CPU resources since BGP will consume resources as it prepares BGP updates for each defined neighbor separately. In order to work with BGP peer groups you add neighbors to a group and then configure/apply all necessary configurations to the peer group.
To see peer groups in action take a look at this FlexVPN post: Configuring & Verifying Dual Cloud & Dual Hub FlexVPN