I think there are some advantages if you set LOG_ARCHIVE_DEST_2 to ENABLE , let's suppose you are performing switchover, during this task initially end of redo will be transferred from primary to standby to complete the switchover to complete transitions of roles. However after switchover you have to ENABLE again if it is already set to DEFER. so of course you can avoid such post checks after switchover.
And if you are using cascade standby, then however you are enabling destinations from standby, apart if destination pointing to primary database, they will be rejected by primary because standby control file only receives it incoming redo or archive. I think probably you may get some warning/informational messages as "remote archiving failed/ rejected by RFS"
I'm not sure why I feel a bit odd calling you 'CKPT' rather than your actual name but I guess that keeps you a bit anonymous so I'll just deal with it. :-)
Your first point is understood and I agree that if the STATEs were set to DEFER that I would have to go in manually after the switchover and set them to ENABLE to get the new Primary sending data to the new Standby(s).
Your second point is very interesting in that since I have only a single Standby site I don't often (if ever) think about having multiple Standby sites and what that scenario does to my switchover/failover plans. I guess I would designate a particular database to be the 'Standby of first choice' and have that one set up so that the DEST_n parameters are pointing to my other Standbys so that when I did a switchover to that Standby it could take on the role of passing all the log changes to the other Standbys.
As I think about it, I guess all the Standbys would be set up that way such that any of them could become the new Primary.
I realize you mentioned 'cascaded standby' in your post even though I was thinking only multiple Standbys in my comment. I agree in that scenario that having the STATEs set to ENABLE would be needed to allow the first Standby to ship log information to the cascaded Standby.
It just shows I need to expand my thinking beyond what is needed in my immediate environment.
Thanks very much for your feedback. It is this extra effort by those of you with more and varied experiences than those of us asking the questions that makes this forum so valuable. I truly appreciate your taking the time to respond.