If I create a calculated metric, I get a preview of the trend like this:
I want the same in segment builder, a line for views, visits and visitors. Perhaps a toggle, dual axis, or normalised view would be necessary.
I want it because it will help me understand the data I'm including in the segment I have defined.
I also want it because of the sequential features in segments. Often I will just pull out a trend in a report with the segment overlaid to see what I'm including in the report. To have this in segment builder would save so much time. It would also help us to understand the new "before/after sequence" settings.