A well-designed Handbook can be a perfect guide to the company’s culture and vision.
Some companies have handbooks more looking like a company presentations. Those are 10-20 pages PDF with fancy pics of the founder or the brief history of the company. It’s better than nothing, but a really good handbook is a guide in the first place, not an ad. It describes the company, its values and rules in a way that every employee can be fully autonomous when trying to understand something big about the company.
The most impact handbook does during the employee onboarding, when newcomers get a clear understanding of how things work at the company.
Several good examples of a handbook in a technology company: