Well they do add to your totals for what level you are on a certain route or a level for a certain loco. In some cases this is needed for trophies (when they work). Also if you speed you don't get points (or miles added to that loco). In one of Matt's streams he once explained it is to give you an idea of how you are progressing and it's not useful for everyone but some like to know. I think though that in the TS2019 it seems to give you a lot more detail on how you drove as well as points (from what I can see in streams, I don't own TS2019 myself). I can see for example my highest rated engine is the M7 on LIRR and that's all done via the points.
Good to know, i ask this because i found an exploit to spam a button to give 15 points per press. So you can spamm it like hell. But if it doesnt give exp then its useless lol