It would slow down how fast cars drive on the road and it would give more space to bikes and most importantly to pedestrians.
It's already pretty slow as it is during large portions of the day. Pedestrians have plenty of space on the sidewalks (except for where the ugly SilverLine head house is by Via). By most accounts, the sidewalks can be considered wide. Bike lanes look pretty standard to me. Certainly not any narrower than elsewhere and I don't see backups happening in the bike lanes.
As posted above, the wider lanes at least give a chance for traffic to continue flowing when so many Ubers/Lyfts are dropping off and picking up (which I find completely annoying as well - see Sleeper St.). I don't think narrowing lane space solves or improves upon any actual needs.