The drama of something to argue over with their Establishment sister party, perhaps?

It is plain that the Democratic Party doesn't want Sanders voters if they're going to demand Sanders policy outcomes. There's no drama in successfully helping people, and what kind of partisanship isn't made of drama?

It is plain that the GOP didn't want Trump voters until Trump more or less took over the ticket with the help of professional-class journalists looking for... drama.

I think that it hurts the GOP more than it directly helps Democrats. In my mind a sudden large increase in voter turnout may give sway to candidates running as Democrats that may not be totally in line with the DNC as a whole. You're seeing a huge leftward push by Democratic voters in the presidential election, and while I don't believe it's as fragmented as the GOP currently is, I don't see any reason why this split won't continue.