1 to 2 dimensions + 1 metric or 1 dimension + 2 metrics (specific case)
Lines are primarily used with a time dimension on the x-axis and allow you to observe the evolution of a metric over time. It’s possible to add a supplementary dimension, where each value of the dimension is represented on a different line. The lines can represent different metrics if it makes sense and they share an axis in common.
A simple example
Let's say you want to compare the amount of video likes and dislikes over time.