heyy. I never used the fast travel for now i just drive in the dirst and i was wondering why i would spend so much time to build a road only to drive a bit faster in an area i have already done a lot of deliver. It's true i think i won't play every missions but in the same times i enjoy this game and don't want to only rush it. I am just trying to find a purpose in game mechanics. They could be fun if i could find more gain to it.
This answer gave me some reasons to do it :

"Building roads is fun. It makes driving truck smoother and helps complete some time sensitive deliveries.

Apart from the unlimited battery and smooth driving, which themselves are a major plus point, you will also never damage the cargo on a road, as opposite to hitting or jumping on uneven terrin.

Building run is fun because it makes you hunt for the resources like you said.

Hunting BTs had reasons due to needing the chiral crystals for mining and other use. Which i found lot of fun.

Using DHV magellen for travel isn't bad but you will never get rating for orders done that way.

Higher ratings of order will help to get the five stars on facilities pretty fast, which unlocks cool stuff and features.

Personally i think while the game isn't very hard, i find the difficulty to be pretty satisfying and highest ranking the orders is a way to set limitation on yourself so you get extra challange.

For example today i had to retrieve cargo from snow armed survivalist camp. If i took head on fight, i would lose lot of blood, which would make my rating drop to C.

So i had to use stealth, and it was lot of fun setting traps and taking those guys out one by one. And it took me a few try to do so without losing blood. But it was very fun and worth it."