Why it matters
Brands decay by a thousand small liberties: a stretched logo here, an off-palette flyer there, a rogue tone in support emails. The guide is cheap insurance: it lets vendors, new hires and other teams produce on-brand work without you personally policing every artefact.
How it works
The useful guide is short, visual and opinionated: the assets, the rules, the common mistakes shown crossed out, and where to find the real files. It lives at a link everyone knows, not a PDF nobody can find. (Its beefier siblings: the design system for product, the verbal identity for words.)
What to do about it
If yours is a 60-page PDF from the rebrand, distil the ten rules that get broken into one page and circulate that. Guides get followed in proportion to how easy they are to consult.