Originally Posted by
rpenmanparker
Sure you do, but gearing is still arranged to allow two ranges of gears one on the big ring, one on the small. Double shifts occur when moving between the ranges, which is much less frequent than shifts within the ranges. Most shifts are within those ranges, not between them. If I am wrong about that, just say so.
Depends on where and how you ride.
Up here, lots of rollers that you can only charge half way up with momentum from a previous roller. So you're in your 50x23 or 50x25 at a reasonable cadence, and want one more gear stepping down you'd double shift (and Campag or Di2 IIRC multishift in back) to say a 34x16 or a 34x17. Something I do many times on a daily basis.
The alternative without either double shifting (or multishifting)..is either grinding in a sub-optimal gearing/cadence, or needing to do 1 left hand shift
and 5 right hand shifts which takes a good bit longer.