Yes and no.
I spent several years in speech therapy in school. I had trouble pronouncing Th, Sh, S, soft C, and Ch. Part of my therapy involved saying tongue twisters, like "She sells seashells by the seashore." That did not help me to get better. I finally quit in 7th grade (I don't know how I got away with that, unilaterally changing my IEP.)
YEARS later, when I had kids and one of them had a speech problem, I realized what my own problem was. Once I could *hear* the difference between the proper sound and the improper sound could I tell what I was doing in my own mouth to produce the improper sound, and then fix it to (better) make the proper sound. (My teeth do not fully close at the sides, so I will never get a perfect Ch or Sh.)
Saying tongue twisters will only help one practice the pronunciation one has. It doesn't *fix* pronunciation.
However, if one has figured out how to pronounce the sound correctly, tongue twisters are a great way to practice making that sound over and over again, and quickly. One must start off very slowly, taking care to form each sound correctly. Just going fast will contribute to sloppy pronunciation and do no good.
I think also tongue twisters *can* help in conversation because they do loosen the muscles and help to create a pattern of speech for certain words. It would make it easier for words to come out, if that is part of what is contributing to conversational problems.