from what the SP lore goes - jumpgates are build over jumpholes. - it is not said if humans themselves are able to initiate jumpholes though - however, once open, they cannot close them at will.
jumpholes are chaotic. - they are unpredictable - and if RP was made seriously.... anything bigger than a fighter would have to have an extremely good reason to go through them ( including anything bigger than a freighter in terms of transportation ships )
i think orillion states, that the jumpholes are unsafe and he really hates to fly his ship through one - which might cause a lot of anomalies that can even lead to the severe damage of even destruction of a ship - and it appears that the greater the mass of the ship, the unsafer the passage through a natural jumphole.
now, jumpgates keep the chaotic nature of jumpholes under control. - that way the huge transports ( which the gates are made for primarily ) can pass through. - even the bigger battleships can pass ( but they don t - vanilla 1.0 places the battleships as stationary objects only )
from the intro, we know that humans even know how to build jumpdrives without the need of a jumphole / jumpgate - so maybe the battleships are rather equipped with a jumpdrive than a jumphole ( but the fact that in the SP, the osiris uses a jumphole, speaks against it )
anyway - jumpgates just control jumpholes - and serve the further purpose to lock them if needed.