In any case you should draw lots in CAW and not in EiG (usually with grid turned off) so as long as road is straight you will get it to line up. You should not by any chance have lots overlaping roads or paths, so it is much much easier if roads are lined with grid.
As far as rendering goes it will create routing issue if lots are overlaping road, and if not lined with grid it will cause that little extra processing to calculate the routing, which is not significant on its own, but can add up to make a difference in game, specially with weaker PCs creating a lag. Same goes with Non Camera routing, if you mark it straight with grid it should be easier to process it then if you have uneven edges.