You won't have to pack heavy winter clothing. Attractions are crowded. Hostels are crowded. Crowded trains and buses, and costs more than in the off-season. You'll meet lots of tourists.
Hostels are less crowded and sometimes have a reduced price.
You'll meet lots of world-wide and domestic travelers. You shouldn't have to do laundry as often, if you aren't stinking up your clothes with sweat. Some attractions are closed or have restricted hours. Not as many hostels are open and sometimes curfews are earlier. Less frequent trains and buses.