Fast growth is intrinsic in the definition of a start-up company. There are several schools of thought on required growth rates for different types of companies in different stages of the journey, but Paul Graham provided an even simpler formula.
A successful start-up will have a growing growth rate.
For startups at least, you want to reduce f''(x) to a single bit. I.e. it's worth caring whether your growth rate is itself growing, but not worth caring how fast.