Comment 9 for bug 306979

Another thing to consider is that when saturating the outbound bandwidth, TCP ACKs of other connections will be delayed, which is one of the reasons why maxing out upload will negatively affect download elsewhere as well. This also applies to any kind of outbound interaction that typically expects relatively low latency. Throttling even a little (to leave room for these low-bandwidth communications) improves overall latency a great deal.

Some users heavily affected by bufferbloat may also wish to throttle more aggressively to better map the real end-to-end link bandwidth (as opposed to filling up buffers midway then blocking entirely for several seconds until they clear up, creating visible high-lows in transfer rates).

I don't think Déjà Dup should be directly responsible for throttling per se, though duplicity probably shouldn't either. I believe the suggestion of composing duplicity with another *nix-y utility is a good one. Be it trickle or another program (possibly a new tool if Déjà Dup has special needs, though I would imagine not).