If people judge books by their covers, they judge diagrams by their tidiness.
People use aesthetic cues to determine how legitimate, trustworthy, and useful information is. Your job is to produce a tidy representation of what you're trying to convey without designing it too much or polishing it too early in the process.
As you make your diagram, keep your stakeholders in mind. Will they understand it? Will anything distract them? Crooked lines, misspellings, and styling mistakes lead people astray. Be careful not to add another layer of confusion to the mess.
Make it easy to make changes so you can take in feedback quickly and keep the conversation going, rather than defending or explaining the diagram.