These machines would allow you to listen to a sentence as spoken by a native speaker, and then record yourself speaking the same sentence.
I have noticed this type of learning being very helpful for me trying to get practice using grammar in a new language. Hearing a native speaker order a sentence of conjugate a certain way get my brain used to doing this in the new language. After practicing this, the next time a run into a sentence structure similar to the example I am more comfortable implementing it.