Diference between Steady SYNC light and blinking SYNC light on 2000's NEXUS?

Steady = in Sync... blinking means CDJ is not in Sync (as in you probably gave the jog dial a push to adjust) however the only useful function of Sync is there's no need to touch the tempo slider anymore if your tracks are properly analyzed on rekordbox- note you can adjust the beat grid directly on the CDJ2000nexus while the track is loaded- push & hold the scroll wheel next to the screen then move clockwise or counterclockwise to re-align the beat grid. 

Even if your tracks are slightly off the main 'kick' on rekordbox the CDJ2000nexus will only match the "red" lines to the "master" track/player

MADJAM - you can alter the beatgrid but you can only shift it left or right and not change the spacing which i think is flaw on the deck. You're right in you could make an adjustment of the grid but if the grid actually needs expanding or contracting when you come to mix out of the track it will be wrong at the end. If Pioneer could implement the full beat grid adjustment that would be really good.

I never use the sync in fully lit mode, creates loads of problems.  I hit play then move the jog wheel, this puts the sync into flashing mode, I then re-cue and play as normal without problems.