Of the 4 listed, I would say the primary objective is identifying a trend in the data to know whether the data is moving in a specific direction—increasing or decreasing in value.

I already added linear regression marks that draws linear regression lines with confidence bands[1] to my Observable plots but they do not give me a “value” so I need to manually look at the graphs and read the red line.

[1] https://observablehq.com/plot/marks/linear-regression