How do you decide when to upgrade your tech in your business?

I was thinking about this in the context of small business or start-ups that have to run lean (at least initially) and wondering whether people upgrade in advance of needs or upgrade when they have to because they come up against the constraints of their devices. Constraints could be speed, processing power, physical hardware like number of monitors, or more enterprise considerations like having multiple devices governed by a central tech policy. Wondering how companies out there are doing it and how long they "go it alone" before consulting experts.