Alan,
I think useful is an understatement. Being able to label lines by attribute would be a huge improvement on current options which frankly are too tedious. There could also be increases in the field from labelling by attribute.
Example, for walls and fences, on all of my topo's I am required to indicate material, type of fence,height and condition all of which can be surveyed as attributes in the field(accepted that fence type/material can be dealt with by use of a unique field code) but can not be labelled in the TBC. Another example might be Kerb where the type i.e. bullnose, splayed, concrete, brick, stone etc can be assigned by attribute and labelled on the drawing accordingly. Currently it is necessary to have an individual code for each type, and layer for each type to be able to differentiate between the various types in the drawing. Lets not forget most clients cad systems can not access the attribute data as in TBC.
Rather than having to use a unique code in the field to distinguish between fence types etc, a single code "F" might be used for all fences. The attribute data would be labelled on the drawing to distinguish between the types. Perhaps a layer could be controlled by attribute to push each type of fence into respective layers if that's what the project brief requires.
Having one code might make it possible to display nearly all codes required for a project on one group in trimble access measure codes. Imagine the efficiency gains from being able to do so.
Still, the biggest issue on labelling from my perspective is being able to export the cross and level value as displayed in TBC, which is currently not possible.