According to MSDN,
MSmerge_genhistory contains one row for each generation. A generation is a collection of changes that is delivered to a Publisher or Subscriber. Generations are closed each time the Merge Agent runs; subsequent changes in a database are added to one or more open generations.
Reading the above, it seems logical that all generations should have a number of changes. However, when I try to select rows from MSmerge_genhistory, I find a lot of them where the changecount column has a value of 0.
Do these rows indicate a problem? Why do generations exist if no changes are included in them?