It is so much more useful in the long run. The students can have an electronic copy of the lesson (before and after), you dont waste time "rubbing stuff out", you can come back to items whenever you please and you can reuse material so easily from lesson to lesson, year to year.
That is before you consider the inbuilt (and other) functionality the electronic whiteboard offers. In our case we have built in transformation tools, on screen rulers, protractors, compasses, graphing facilities etc. Then when you branch out and use apps, websites etc the amount of interactivity and usefulness increases massively.
This never replaces good old fashioned teaching and knowledge and methods, but as an added bonus it can be massive.
However, at the end of the day, you cannot do proper mathematics without resorting to proper work on paper, with a pen or pencil and a bit of brainpower and a lot of patience. That will never be replaced electronically.