Can someone tell me what the point of running LACP or PagP between two switches/routers for ether-channel is? My feeling is just set up the links on each side and set the mode to "on" and be done with it. It seems like running a protocol to do this same thing just causes unnecessary traffic between the links.
I use layer 3 port-channels (ether-channels) and have never enabled PagP or LACP.
It's really a function of preference . PAGP and LACP will check to verify the channel - trunk parameters match on each and won't bring the channel up if they are incorrect . As another poster said there is specific warnings about the "forced on" mode. Myself we usually do use either PAGP or LACP unless restricted by say a server nic that does not support either protocol. I have not seen where it causes any kind of delay bringing up the channel , it comes up almost immediately. The traffic generated by these is minimal . If you want to use on thats' fine too. You will find even varying reccomendations in cisco's best practice docs , some say to use PAGP or LACP and other say to use "on" so take your pick .