When playing tunes, jigs/reels etc, there is a generally accepted convention that a number of these tunes are played together, in a set. I assume that this practice has it's origins in the fact that these types of tune were originally played for dancing?

Would it be right to think that as the dancers would sometimes like a particular dance to go on longer than an individual tune would (usually an A and B part, played three times), that new tunes were introduced, in sets?

Was this introduction of sets to enable the dance to continue and to prevent the musicians from becoming bored, or was this to mark changes in the dance?

What were the conventions for this? Where all tunes in a set, the same dance or did they have to be all reels or jigs or all polkas?

Now that these tunes are not played exclusively for dancing, the practice continues but do the same conventions now apply? And if they don't, should they ?