You can answer this question by first describing how impeding calls function and why they are used within a JavaScript program. You can then describe the advantage of non-hindering calls and the benefits they provide. Note that the question asks you how these relate to Node.js. Make sure to include this in your answer. Many candidates don't listen to the complete question and neglect to provide the information the interviewer asks about.

"Impeding calls are those where the execution of extra JavaScript needs to stand by until a non-Javascript activity is completed. This is an example of coordinated activity. Non-hindering calls can execute non-concurrently and will be faster. This is important since JavaScript is single-threaded and serially, using a single storage stack. Most of the I/O operations in Node.js use impeding calls. An example is executing fs.readFileSync, which results in the reader being fully executed before the program proceeds."