You can use the Line tool to adjust many automation parameters, eg. Frequency Cutoff, volume etc.
What I can’t do is use the Line to to add automation for things like Insert On/Off and pattern select in certain VSTi’s. For those things I must use the pencil tool.
Why not allow both the Pencil or the Line for all automation and keep things nice and consistent?
The reason I’d like to use the Line tool is that it snaps to your Grid settings whereas the Pencil does not.