George there are several good reasons. if for some reason the loop gets broken, you'll loose the devices beyond the break in the wire, not terrible if it can be fixed asap but that hardly happens that quickly.With a class "A" system the F.a.c.p is setup to see the break in the loop and start polling the slc loop in both directions so your devices will not go missing from the loop. another reason is the eol. for some reason the as builts are never accurate in where they may be, and if you've ever been in a super market searching for the eol on a h/s circuit you'd swear to yourself you'd make the next install a class "a" system to avoid that hassle.
