Cumulative versus monographic dissertation
If I had had a choice, I would have chosen to write a cumulative thesis. 

Results are in the papers. And converting papers into a monograph takes a lot of time with relatively low added value. (When someone asks me about the result I still point to publications.)

One advantage of monographic thesis is when it is on a new field (with publications being very coherent on one topic) - then it can serve as an introduction for the others. (However, it seems that not many theses fit this criterium.)