Angela writes, "I am a US citizen and I want to sponsor my husband for a green card but because he is completing his education, he and I live separately. We plan to live together once he graduates in a year or so and finds a job. Would this be a problem for his approval?"
Indeed, it will raise a red flag but as long as your marriage is genuine, there is nothing to fear. For the interview, you will need to have not just evidence of your wedding, but other evidence like vacations, family reunions, record of phone calls to each other, and things like joint bank accounts/retirement plans/insurance policies, etc. The USCIS officers are not stupid and they understand that some times couples may be separated for genuine reasons, so what they are looking for is good evidence of a genuine marriage. You should work with your lawyer to come up with a list of documents that you can present with the application and at the time of interview to prove that there is no marriage fraud.