I don't see much value in knowing the factions except for a tool that also tracked my reputation with each one (and therefore could have it's own data gathering for both factions and reputation). So I wouldn't bother with storing factions for TGC. Overall allegiance is worth doing though. And yes I guess these things could change over time, at least through FD scripted events.
You might if it's a major faction that you've peeved off. Or indeed the opposite of if it's a major faction you're popular with, so know you can get reduced repair and refuel costs.