Beat matching is an art where DJ’s seamlessly blend two songs together by starting a new song before the old one finishes. For example you will be dancing to one song and without knowing it you are dancing to a new song in the same tempo as if the song never changed. This is a nice skill for DJs to have but ultimately is not crucial as it all boils down to the song selections. As long as people are enjoying the music played and that there is no “dead space” in between songs then seamlessly beat-matching from one song to the next is not a deal-breaker.
Another common song transition is called a segue. A segue is similar to what radio stations do. As one song is about to end they start another so there is no “dead space” in-between the music. These songs do not necessarily have the same tempo and most of the time is easily identifiable when a new song starts. As long as the music is good then the listener will stay tuned in. This is the same concept for mobile DJ’s, as long as the music relates well to guests they will stay on the floor.
All in all beat matching is a nice skill but should not be a prerequisite when choosing a DJ. Look at the DJs past references and talk to their past clients. If they were happy with that DJs service then they enjoyed the music. In fact most of the time they wouldn’t even know if the DJ beat-matched or just transitioned with traditional segue’s or did a combination of both at their event. Ultimately they just remember if they had a good time and if they enjoyed the music.