Why use the price-to-book ratio?
In a nutshell, a lower price-to-book ratio could indicate that a stock is undervalued. When you're comparing two stocks with similar growth and profitability, P/B can be useful for determining which is the best value at a given moment.
The lower a company's price-to-book ratio is, the better a value it generally is. This can be especially true if a stock's book value is less than one, meaning that it trades for less than the value of its assets. Buying a company's stock for less than book value can create a "margin of safety" for value investors. However, a very low P/B ratio can also be a sign of trouble at a company, so it should be used as part of a thorough stock analysis.