Originally Posted by
Koyote
... Why bother with two chainrings if they're so close together?
It's half step gearing, with the rear jumps of 14% and front jumps of 7%. This style emerged in the days of fewer cogs in the rear with wider range jumps, and a half-step double or triple on the rear to give the smoother transitions between. It works a charm once you've learned and committed it to muscle memory. Very nice.
By the way, to the OP, I'd go 42/45 with the rear 14-34 that you've described.