For those thinking of trying 10.10.4 on a 2015 rMBP, there's at least one gotcha: Copied from Radar 21325956
The scaled resolution in system preferences does not function properly in 10.10.4 14E33b. Each of the resolutions is misplaced , and they are out of order. Resetting the SMC does not correct the situation. S
Resolutions are in this order:
1280x800
1600x1000 (blurry)
2048x1280
1024x640
1440x900
1600x1000 (one step up from the default in 10.10.3) appears to be blurry in 10.10.4.