Key point
One job
A chart label should remove guessing. Your viewer should know what is measured, the unit, the time period, and the main takeaway without asking you on a call.
For a hackathon demo, assume a recruiter or judge sees your dashboard for 20 seconds. Labels must carry the story.
What to label
Every useful chart needs a clear title, axis labels, units, and a time range if time is involved. If the chart uses categories, make the category names readable.
If one number matters most, label it directly. Do not make the viewer match colours to a legend when there are only one or two important lines.