The funny thing about travelling in hyperspace is that, if you’re fast enough, you can overtake the ship you’re chasing and they won’t know it until they drop out again. With the ability to predict the course a ship or a fleet will take through hyperspace, anyone with a gravity well projector could theoretically not only pull it back into realspace, they could do it anywhere along the path, provided they can reach it first. I expect you could also reroute a ship equipped with a gravity well projector into the path, if your own ships weren’t fast enough. If the First Order acquired an Interdictor-class Star Destroyer, for example, they could drop the Resistance fleet right in the middle of their navy. 

I’m sure there are other creative uses for those two technologies, but that’s what came to my mind. 

~ Jacen