In case interviews, is it acceptable to go down a "branch" before exploring other branches, or is one expected to follow through each branch in parallel?

One thing that helps is to try to avoid going down the wrong path by saying things like: "I would look at ____ to see if that is an issue, unless we know that is not an issue." Usually the interviewer will steer you away from wasting your time if you are way off the beaten path. or even "Now that we found ____ is an issue, I'd like to look at ____ and ____. Any preference which we should look at first?" If phrased well, the interviewer will probably just tell you which path to go down.

You can't go through all the branches - there simply isn't enough time. If you try, you'll end up giving at best a very shallow answer on everything and you'll never get into the real meat of the case. In most case interviews, there are usually one (or more rarely, two) really important issues that you need to identify and resolve. This is similar to an actual case, where typically a small number of issues disproportionately drive the results. Hence, the skill of identifying and focusing on the most important issue is one of the key skills that the case interview tests. A good way to do this in a case interview is the ask for more information at a high level before you drill down more deeply, and then focus only on those areas that are important. To illustrate, let's use your hypothetical profitability case, obviously simplified quite a bit. Here's how I would approach it: Interviewer: ClientCo's profits have fallen over the last 3 years. What do you think might be causing that? You: Well profit equals revenue minus cost. How have revenues and costs changed over the last 3 years? Interviewer: Revenues have increased from $100M to $102M. Costs have increased from $80M to $98M You: That's interesting, it appears that costs are the main issue. Costs can be broken down into fixed costs and variable costs. How have each of those changed over the last 3 years? Interviewer: Variable costs have increased from $60M to $77M. Fixed costs have increased from $20M to $21M You: So variable costs have been the main driver... And then you get into the meat of the case, which might be about changes in raw material prices, falling labor productivity due to higher turnover, or whatever. Two key takeaways: At each stage, identify for your interviewer the full set of options you could explore. (To show that you are aware of all the possibilities, since you have no way of knowing beforehand which might turn out to be important) Before diving into any of those options, test which one is most important, and focus on that.

Actually two said ways are both acceptable: to go down a ”branch” is so called Strategic hypothesis by Roland Berg, to follow through each branch is even more famous: MECE by Mckinsey.   I think the arguing between these two method is: which is more efficiency? That depends on who to use it.   If you are a rookie solving questions from an unfamiliar field, u need MECE. Because it helps to make sure nothing is left.   Strategic hypothesis is recommended if you are already an expert to a field. Suppose that I am an operation expert in your profitability case. Base on my rich experience I guess, that this company may have problem in the branch 2bb”price”. This hypothesis is based on my experience ,my judgment, and I know it is probably the right direction. That could save me lot of time if I was right. In this case, to go down a certain branch(which selected by expert, but not just any branch) is much better than MECE.