Knowledge bases are systems used to aggregate and categorize information. They are very useful for many kinds of organizations - SMBs, NGOs, and even freelancers. This is because knowledge bases are very versatile - they can contain any kind of data imaginable, from internal company policies to cooking recipes. Wherever you work, you probably regularly have to give out the same information on a regular basis. Maybe customers often e-mail your support helpdesk with the same questions, or maybe new hires always need to be given the same orientation talk - either way, you can use a knowledge base to reduce time spent on these repetitive activities.
With a customer-facing knowledge base you gain a 24/7/365, fully hands-off support channel; if you choose to start an internal knowledge base, the training time for new employees can be cut down significantly. Basically, there is no excuse for writing down the same answers multiple times - do it once, and share them forever.