Quando usar um Line Chart
You are showing change over time
Revenue by month, users by year, temperature by day. Time on the horizontal axis, the measure on the vertical, one point per period.
You have many time periods
Twenty-four months as bars is a fence. As a line it is a shape you can read in a second, including where it turned.
You want to compare a few series
Two to four lines on shared axes make relative growth obvious. Whether the gap between them is widening or closing is visible without any arithmetic.
The rate of change matters
Slope is the one thing a line chart encodes better than anything else. If accelerating or flattening is the point, use a line.