I'd like the option of being able to be at peace longer without random events thrusting me into war.
For example, at the 1900 start I am unable as France to make it to 1914 without at least a war or two, and similarly cannot make it to 1939 in the 1920 start.
I know that's not everyone's cup of tea, but one benefit would be the naval treaties actually mattering. As it is, the navies never reflect treaty limitations as there will be a war before even the first treaty ships are launched.
I've played "no war" RTW1 game a month ago, so it is possible there. For Russia, I needed three restarts (Japan like to surprise their rival too much - even at point below orange tensions) and finally ended game in 1930 with 31 prestige. Even two DDs blown at anchor and mysterious sub attack didn't cause the war, though I spent ton of prestige to solve those events peacefully. The key was to keep most nations at lower end of yellow bar (so any decision except ultimatum doesn't cause war immediately) and don't do anything reckless. If RTW2 don't have many new "no choice" events, peace-keeping should be possible here as well (with some luck). The cost of peace, as dorn mentioned, is another question...
The issue I have with that is that it either makes the budget minuscule or lowers prestige to the point where a random event can cause a game over.
I would like to have new Ferrari for 1000 dollars. :-)
Frankly, If you have lower tension, it is logically that goverment will spend less on military. And peacemakers never get prestige they deserved. ;-) You cannot have everything, you need to choose. Usually war/budget/prestige vs. low tension, low budget, low prestige and it is quite logical.