One of the most fundamental ideas in strategy is that success comes (partly) by investing in attractive markets. Attractiveness for a profit seeking business is typically defined as being from a mix of size, growth and profitability. Of these, the hardest to estimate is profitability because it is of the market (rather than your current profitability - which might be more or less than the average for the market). Porter's Five Forces is a famous framework that allows you to estimate, in a qualitative way, how profitable a segment is likely to be.