there is no general answer for this – it could be either of the options. Also, even if there was a most common type, it would not make sense to consider it as starting point without any further check. The best thing you can indeed do at the beginning of a case to verify which area to investigate is the following:
- Segment by profitability/revenue channels. Ask the interviewer how the client segments its profitability channels (by product, customer, geography, distribution segment, etc).
- Identify which channel is the priority. Ask for the change in profitability for each channel. Then start from the one that had the biggest decline in profits.
- Identify whether it is a revenue or cost issue. Ask how revenues and costs changed for the channel that you have identified. Start from the area which has the major negative change in absolute amount
In this way you can be sure you are always analysing the right area.