Sentence fragments are okay, dialogue does not have to be grammatical (it would likely be unrealistic except for a grammarian; few people speak grammatically correct sentences all the time).
What you want to avoid is blatant grammatical mistakes that would make a reader stumble and lose the flow of reading.
Pro readers are not checking your grammar! They are checking to see if your story reads smoothly and holds up and is taking them for a ride. Bad grammar may interrupt that experience. Sentence fragments do not necessarily, if they feel like part of the ride.
So I would use them for emphasis only. Do not use them as shorthand to try and pack a lot of character description and camera direction into the exposition and still make it look short. That won't fool anybody, and will seem amateurish, and will break their flow and ruin the ride.
Use them as emphasis, or perhaps to give a sense of rapid action. I might use them for the latter in a cluster, but wouldn't use them more than a few times in the script. If you feel like you must, you are probably trying to control too much and write too much that isn't your job, it is the job of the director or various effects people.