Many philosophy problems involve imagining hypothetical scenarios. At times there has been significant debate over the validity of this.
At times there has been significant debate on Less Wrong about the relevance or value in discussing hypotheticals that are unrealistic. In The Least Convenient Possible World, Scott Alexander suggests that ignoring hypotheticals often means that you are technically correct at the cost "missing the point and losing a valuable effort to examine the nature of morality". He suggests that considering about the least convenient world is often vital for allowing us to discover our true motivations and often leaves us too much "wiggle room".
In Please Don't Fight the Hypothetical, TimS suggests that fighting the hypothetical is equivalent to, "I don't find this topic interesting for whatever reason, and wish to talk about something I am interested in." He says that this is fine, but suggests it is important to be aware when you are changing the subject like this.
Hypotheticals: The Direct Application Fallacy suggests that it is a mistake to assume that the only reason for studying a hypothetical situation is to understand what to do in that exact situation. It suggests that practise exercises don't need to be real and in fact insisting on this can make teaching nearly impossible. It further suggests that examining degenerate cases of a theory often provides a useful sanity check and can make the limitations of a heuristic more explicit.
Hypotheticals are essentially the same as counterfactuals, although a) the term counterfactual is preferred when imagining someone making different decisions b) technically the factual isn't a counterfactual, but it is very common to say something like "iterate over all the counterfactuals and pick the one with the highest utility" where we treat the factual as a counterfactual.