A)Develop when you have too much of X monarch point ?
B)Develop just only to unlock buildings ?
B)Develop just only to unlock buildings ?
Frankly, development is a nice idea. But it is way too expensive to go "tall" then wide.
Other considerations aside, lets say that the cost of development is at 56 power.
Developing +3 base tax = 56 + 61 + 65 = 182 adm
Conquering another province, assuming low dev one, lets say 9, split equally 3/3/3 = 10 adm * 9 dev = 90 adm, its is about half cost of developing.
Sure I didn't take into account that you're going to have autonomy in the conquered province, but I also didn't take into account the extra 3 base prod and 3 base manpower.
The difference is too big and after improving a few times, it grows even bigger.
If the conquered province has high base tax and lower base prod/manpower, the difference is even bigger.
This means the only power worth using to develop is mil, when you're reaching cap and ahead of time.
Otherwise, it's more much more useful to take another province either by conquest or by diplo annex.