In sketcher, it is often the case that one would like 2 or more dimensions to have the same value. For example, when sketching what should be a set of lines offset from another set of lines, but you can't do that in sketcher. Then you end up making dimensions equal to fake the offset.
One way to make dimensions equal is to write sketcher relations. I don't like to do this, because there is no obvious pointer to the poor soul who comes to modify things at a later date that he or she should look for these relations.
Another way is to insert lines joining the offset lines and apply an 'equal length' constraint to these lines, before making them construction lines. This works and gives a visual clue of what has been done, but it is simply too many hoops to jump through for what is such a simple thing.
It seems to me that there is a case for a new constraint type in the pop-up box that sets an 'equal' constraint, but is applied to 2 dimensions, not to 2 sketched entities.
I can't think of any disadvantage to adding an 'equal dimension' constraint type, but I can see advantages.
There are probably other constraint types that could usefully be added, too. feel free to tack them onto this idea or to raise another.
Please vote up if you think there is the smallest chance it could be of value.