If a concrete slab at your worksite has started to sink, slab jacking is usually a viable option for re-leveling the slab. In optimal conditions, and often in not-so-optimal conditions, too, slab jacking is easy to accomplish and works quite well. But if your worksite has to deal with certain conditions, the slab jacking might not work so well, requiring additional work. To ensure the best results, have the area around and under the slab evaluated so you know whether you can proceed with the slab jacking.
You need to know the reason why the slab started to sink in the first place. If it sank because a pipe burst and washed away supporting soil, and the pipe has since been fixed, slab jacking should work. In this case, there wasn't anything inherently wrong with the soil. On the other hand, if the soil under the slab was unstable and shifted due to a small quake, for example, that's not a good candidate for slab jacking, at least not yet. The soil has to be stabilized so that it doesn't shift again. Otherwise, the slab jacking will just be a bandage on a festering problem.
Thin concrete slabs sometimes don't do so well with slab jacking, cracking instead of rising up. If the slab you have is only a couple of inches thick, for example, you'd have to proceed very carefully with slab jacking and ensure that the slab did not show signs of cracking during the leveling. The slab also needs to be checked for signs of cracking from the initial sinking, too. If the slab cracks, you'll have to remove it and replace it.
One little-talked-about issue is the very minor but still present scarring that occurs from the drill making small holes in the slab. Slab jacking requires that these holes be made, and they should be patched after the job is done. But if you need a perfect-looking slab, for whatever reason (e.g., you're a patio contractor and you want your customers to see a perfect example of your work), talk to the slab jacking contractors and see where they put the holes and how they patch them up. Be sure that any traces of the slab jacking are acceptable to you.
Slab jacking is a really good way to fix a lot of problems with concrete slabs. You just need to ensure that the process and results will be acceptable given certain conditions.