Macbook Trackpad Tap To Drag Issues
It seems like apple moved the option for enabling tap-to-drag to the accessibility pane. You can enable it there:
Note: ticking three-finger drag (in the Trackpad prefs pane) will change the Accessibility-pane setting. Unticking the drag setting in the Trackpad-pane first then follow these instructions to check your Accessibility preferences.
I have "Enable dragging" under Acessibility turned off and "Tap to click" turned on under Trackpad -> Point & Click. Everything both clicking (by tapping) and dragging works on my internal trackpad.
This answer is still relevant (I will update if needed or stops working). Just confirmed it on a new 2016 MacBook: both three finger drag + tap and drag works.
https://apple.stackexchange.com/a/215339/72142