For those who say that its not nescecarry I reccomend trying to read off stuff written by other people, you might be able to read your handwritting fine, but other peoples is much harder, and when we are talking about engineering calcualtions it is vital that the correct numbers get read off or big time mistakes can happen.
I don't think it was required at the engineering company I worked for last summer to cross sevens, dot zeroes, and cross "Zs", but everyone did it, and so do I, it just makes it that much easier. On a somewhat less related topic, I also use many different script letters and greek letters in engineering calcualtions. I use a different "T" for time, torque,parametric equations, and normal text. I use differnet "F" for fourier transforms, generic functions, or standard text. Use different "L" for Laplace transform, length, and text. And of course pretty much ever greek letter upper and lower case has some meaning which I use. Like upercase delta is for a change in a quantity, lower case delta is the dirac delta function, or partial charge on an atom. Uppercase sigma for summation notation, lowercase for resistivity, stress etc.
I guess it isn't really all nescecarry, but the way I feel, the mroe different symbols you use, the less chance you mistake one thing for another.