Switching from a large company like PayPal to a startup like qunb has been challenging in many ways for me. Design tools and methods are heavily used, shared and documented accross all the design teams at PayPal. That was not really the case at qunb (as I think in most of the startups).
Yet, I think that these tools are probably more useful for a startup than for anyone else.
Things go fast there : everybody is trying a lot of different ideas, work is delivered quickly to the users, doubts are often in minds,... all these specifities make it easy to lose the vision of a product, and to forget existing design decisions, the reasons why we are there.
Losing its direction is, in my opinion, one of the most important danger in a company. If you don't know where you go, if you follow blindly all the ideas, all the signals (a customer feedback, an investor advice,...) without being able to put them in the "next" and the "whole", you just end up by runing in all the directions, unable to really move forward. You need a standard process to digest all these insights and to put them in front of the design vision.
A design method is a good way to frame design decisions. It's not about visual guidelines, interaction patterns or design principles. It's about a process to follow to be sure that every decision will go through the same steps before making a choice.
This design practice has been created with this goal in mind.
Don't hesitate to have a look at other case studies.