I recently bought my first kayak (yeah me - a Perception Sierra) and
have been transporting it by strapping it upside down to my Thule
bars. It seems to work well. But everyone I see is using some sort of
kayak attachment on their Thule/Yakama bars: saddles, j-bars or
stackers, etc.

I can see where these might be useful with a nice fiberglass sea kayak
or if it's necessary to carry the boat on its side. But do the
attachments add anything with an inexpensive plastic kayak? I fail to
see how strapping the kayak to bars clamped on the crossbars would be
any more stable than strapping them to the crossbars themselves.

What am I missing? Thanks for any help,
Sal