Established rules for the universe:
- FTL travel exists with special drives, special artificial generated wormhole like tunnels where space ships can break the laws of physics.
- Engines runs hot, burning at max (top ~10%, depending on tech) for too long will make the engines overheat.
- Engines requires the same maintenance no matter what speed they are running (unless they are running hot).
- There are no time distortion based on space travels.
- Traveling in the wormholes can vary from time to time (the path of least resistance applies to wormholes, sometimes that causes the wormhole's length to vary because of loops)
- Fuel cost if any, is not of significance.
Why would a space faring nation fly at lower than max-cruise speed
It is often seen in sci-fi that captains, order speeds lower than max-cruise speed when flying. Not considered propulsion engines that could be used to leave orbit, planetary systems or other obstacles but Warp, FTL engines that could move the ship safe from A to B.
Would there be any logical reasons for flying slower than capacity except from the obvious "we have to arrive in 5 days and the travel takes 3"?