Beat Matching is an important part of the foundation for any DJ. Before the introduction of computer based syncing of beats, a DJ needed to learn matching tempo and start time of beats to being able to mix tracks together.
Even though the sync button does not require DJs to learn this skill anymore, we still see it as an essential part of understanding beats and timing. Besides that, beat matching for many DJs is where a big part of the fun in DJ-ing lays. The adrenaline that rushes while you are trying to keep two or more tracks in sync is like no other.
We highly recommend learning beat matching.