Haswell (and Broadwell) lags/pauses/unresponsiveness shortly after boot (and after wake from sleep)
Shortly after login (and somewhat prior to login), the mouse and/or graphics may seem unresponsive. This usually clears up after about 20 seconds. The same effect is observed after wake from sleep.
May be related to SMBIOS changes, as similar effects were observed when using MacBookPro11,2 with previous versions of OS X/macOS. But now the problem appears also with MacBookAir6,2 and MacBookPro11,1.
The solution appears to be removing unused connectors from the ig-platform data in the framebuffer kext:
https://www.tonymacx86.com/threads/...s-in-10-12-sierra.202316/page-94#post-1485104
Note: In some cases, this is issue from 10.12 is already fixed in 10.13. YMMV.