The difference between Class A & B informs the game mechanics. Generally it indicates more wealth is likely near Class A, starships typically being more expensive, and usually having physically larger shipyards. This is reflected in the Spaceship Encounters table - where yachts, subsidized liners and merchants are more likely to appear. It also contributes to the rationale for higher DM for military bases to be present.
In game it also can have an impact on PC locations:
- All new starship's first deploy from Class A
- Replacement or upgraded jump drives can only be fitted at Class A
IMTU (CT version), I considered house ruling Class B to support Annual Maintenance for everything but the Jump drive part of any spaceship, but still allowing repairs. This would mean that Drive Failure penalty for M/PP is avoided, but J-Drive remains (+1 weekly). However, Annual Maintenance rarely ever figured in my games.
More abstractly, if only Class A could construct spaceships, then all in-system non-starships would have to be jumped from other systems.
P.S.
Fritz_Brown, 77topaz - oops, I should have written 'Also' instead of 'Otherwise' - the missing option for refined fuel with no shipyard is obvious, so I wasn't trying to rationalize that. The missing shipyard with no refined fuel isn't as 'logically' obvious.
CT described certain ships with drives built for unrefined fuel - so a Class B whose yard customers were Scouts, military and quasi-military (and cheap commercial ships) would have no need to provide refined fuel - hence a logically missing class between B & C.
I didn't address this IMTU, only the Class C with no refined fuel, which I handled on a case by case basis. No 'rule' - just an option. This way I either informed the players that a Class C did have (normally) refined fuel or didn't or that they would have no way of knowing...