Rule of 40
A rule of thumb for software companies: the revenue growth rate plus the profit margin, often the free cash flow margin, should add up to at least 40%. It weighs growing fast against making money.
Simple example
Company A grows 30% a year with a 15% free cash flow margin: 30 + 15 = 45, above 40. Company B grows 50% but burns cash at a −20% margin: 50 − 20 = 30, below 40.