With the new July 2023 update on line chart visual, there are 3 types of lines. Earlier we used to see only 1 line type (i.e. linear line). But now, Microsoft Power BI has included 2 more types: Smooth and Step

Attached is the screenshot for your reference:

If it is important to display the exact values then the linear lines do a much better job but if we want to find a trend and precise measurements then it's better to have smooth lines. And when we wish to show the changes that occur at irregular intervals, we go for the step lines.