It's most likely that it will be an animalistic ghost, and they generally love Soul Pearls and will feed on them preferentially to humans. You can offer safety and food, and that's enough to be worth it. If it's "awake" both the risk and the benefit are a lot higher - an awake hostile ghost could be a problem for me. But they generally are very lost - they're usually quite old - and still need to get qi somewhere. Most reasonable ones will be happy for a guide, at least I think so. Of course people are people, and a lot of ghosts are burdened with memories of their deaths which make them unstable/fragile, so you are always risking being eaten even with smart ones. This is why the Chinese take such a hard line, they basically treat ghost spirits as fundamentally untrustworthy.
A contracted ghost spirit will continuously feed on your qi and chi. You'll feel sluggish, fatigued and sickly for a while before your system gets used to it. It'll also knock a few years off your projected lifespan - but you're a Cultivator, you're already getting a lot more years than most people.
In return, the ghost spirit will process True Qi for you, essentially acting as an additional active dantian. In other words, having a ghost spirit contracted means you can refine True Qi - which is the defining ability of a True Master, the second realm. It's an artificial and limited capability which isn't nearly as good as the real thing, but it gives you access to True Qi far earlier than you ought to be able to have it and that means you can push your way through the First Realm very easily, comparable to having amniotic True Qi or better. Then in the Second Realm it still acts as an additional dantian - which will be a large fraction of your True Qi generation in the early realms - and that means you can break through to more dantians faster, so the overall effect is still major. In the Third Realm it levels out and becomes simply a permanently on weak qi pill (because your qi generation is higher than it should be), but it's still useful. After you unlock the Four Extraordinary Meridians your liquid qi generation swamps the relatively weak effect and it stops being useful.
All of this is with an animalistic, dumb ghost spirit. A thinking one can do pairwise cultivation techniques with you as a Dao Companion and even possess your body to use techniques they knew in life. That kind of help is good all the way to True Monarch, after which it starts getting personal and artistic and inspirational enough that you basically have to do it yourself.