The hanger is the second most important part of the truck
Narrow vs. Wide
The easiest explanation is the narrower the hanger, the more more te truck turns but you’ll lose a bit of stability. A less wide hanger grips a little bit better in corners. To run narrow trucks for downhill, you will want to have a deck that matches the width of your trucks, so everything works in harmony.
The 180s (mm) were a standard for so long, and to this day they definitely have use for freeride, as the slide on them feels very smooth, and they are super stable. The downside can be, that they can get really wide, especially with wide downhill wheels. After that, turning and maneuverability becomes hard.
For other categories, such as dancing and cruise, you can choose narrower trucks, if you are looking for quicker turns or if you have narrow board, that would fit the smaller trucks with ease. Also with LDP (Long Distance Pushing/Pumping) you can find narrower trucks often, which makes pumping easier.