Having good synch at a certain tempo means that you can play each note very cleanly & precise ... Bad synch means that one hand can go faster than the other , which result in unintentionaly muted sounds and overall sloppy technique (no matter if it's altertnate picking, sweeping , tapping or whatever).
As you go faster , your synch on slower tempos should get better ... Practicing with a metronome is the best way .
