Front usually but anything that is visible from the road normally gets them.

I love the farmhouse look too but imo sometimes just black and white can appear a bit stark over time. How about replacing your screen door with a full window/full screen for better visibility of your red entry door? Then I 'd use red shutters for a pop of color and brightness, and put in some reddish pavers or decorative stones leading up to the front door, place plants in similar colored clay pots flanking the door, or use mulch with browns and reds to bring in earth tones and tie everything together.
If you're doing your own install on the shutters, maybe just do the front and see how you like the look for a few weeks. If you feel it's lacking, finish up the other windows that show from the road. If it's an install, I'd print out 2 of above photos and draw in shutters on front only in 1 pic and on both sides showing on the other before you make your decision. Good luck!