In the context of playing for dances, it's common practice but according to John Kirkpatrick's controversial Medley Mania article the practice is neither traditional nor desirable.

So maybe Martin has taken that to heart, but I notice that JK himself plays tunes together as part of a set for listening, I would guess because that's a different situation from dancing.

I rarely perform a single tune, but usually don't go over two, whether it's part of a folk club set or for a dance.

Anahata