I personally do not use this exercise, but like so many other exercises, what we as trainers decided to add to our exercise tool kit depends on our comfort level and philosophy. I agree with Joanne that there are many, many other ways to work these target muscles, and for my money “when in doubt (and there are other, safer and/or more effective options) why do it?”
If you can tell me the reason behind performing a sit-up then I can further assist in answering the question.
Anyway the core is commonly trained through mobility exercises such as flexion or extension. However, from a “functional” perspective – it is rarely how we utilize these muscles. Rather they are used to prevent motion not initiate it.
Fuel the Movement,