Me personally, well I get a wicked pump in my traps. I can isolate pecs only if I focus on that muscle and really squeeze it at the top. I find it much easier to isolate with dumbells. I can decline extremely heavy weight with a bar up to 140kgs depends on the day obviously.
Decline is meant to target the lower pectoral muscle and is also used as an assistant exercise for flat bench as it works your front deltoid so well.