Business is about making more money than has been spent to acquire it, so tracking profits and expenses is what ultimately determines whether a business is successful. There will often be times when money being spent will outstrip profits without an opportunity to make up the difference, but these are often times when capital investment is necessary. The profits should accrue over a span of time, and success can further be measured by how long it takes to accrue them.
The people who start small businesses often have a finite line they need to maintain to keep going, and being able to account for their expenses and profits is essential. Keeping their expenses to a minimum is often best because they do not yet have their own niche, or they might still be fighting to gain a reasonable share of a market. Finding customers is important at this stage, and retaining them for later sales is generally the overall goal to fund their future profits.