It really depends on a lot of factors (i.e. type of business you are in, how much cash intensive it is ...).

As a general rule though, I would advice you to BOOTSTRAP AS LONG AS IT IS POSSIBLE.

Bootstrapping has a lot of advantages, nonetheless that you get in lean mode and make the best of each possible opportunity (or else you are out). Bootstrapping, while building a set of CORE METRICS around your business, will help you realize the real value and potential of what you are building.

As CORE METRICS (revenue, users, ARPU, LT, LTV, churn...) improve, the cost of financing will decrease. So you will be able to get funding on better terms.

Also following a path similar to this, will give you a much better understanding on WHAT YOU NEED FUNDING FOR (besides getting a nicer office). Metrics will tell you and investors will know.

Can you be bootstrapping for ever?. Probably yes (if this is what you want and how do you want your business to evolve), although most probably not advisable. When the metrics are right and you have a fire burning (as clearly seen in the METRICS), I would say it is time to get some petrol and make it much bigger.

Happy to chat about my experience.

Pere