GeoTol Dimensioning (Beginner Question)

No you do not need to, but I would say why not keep doing it? Sure you may have to recall more alignments for other features in reporting. It's good practice to always have in the event you do not use GeoTol it will still work for you using Legacy. With GeoTol if you notice, instead of the Red/Blue/Green Trihedron arrows there is Yellow arrows with Blue arrow tips representing that datum structure if your cursor is on that reported dimension

Here's a picture if you don't mind taking a look. I've been posting this part a lot, haha. I hate cylindrical parts like this. Autolines and 3D constructed midlines are safe, right? I'm not doing any alignment rotations until the dimensioning section. Edit: 3D midline seems to be the only option anyway.

It would be better to construct 2D or 3D widths rather than mid-lines / mid-planes.  Widths capture all of the surface data which...

1. Allows the geometric tolerance command to re-calculate based on the math settings selected)
2. Allows the geometric tolerance to project to the extreme's of the width and interpolate between hits where necessary.
3. Allows you to report the size (width) of the slot and apply MMC/MMB if required by the drawing.

Mid-lines / Mid-planes are treated as pre-resolved features that have no size.

It would be better to construct 2D or 3D widths rather than mid-lines / mid-planes.  Widths capture all of the surface data which...

1. Allows the geometric tolerance command to re-calculate based on the math settings selected)
2. Allows the geometric tolerance to project to the extreme's of the width and interpolate between hits where necessary.
3. Allows you to report the size (width) of the slot and apply MMC/MMB if required by the drawing.

Mid-lines / Mid-planes are treated as pre-resolved features that have no size.

True! I try to use widths. I'll delete the midlines and add 2D widths in my dimensioning section. I think I'll have to do the alignment rotations then because I'm dealing with autolines.