We are designing nothing, excel allows you to create variables with names assured unique in a namespace(A single spreadsheet). You could use it any way you like.

But if you are copying a formula that has things like variable names into a new sheet, you have to understand that pasting the formula with its variables pointing to nothing is like inducing a NullPointerException.

Yes, the point is, this is why people avoid naming things in Excel. Getting them to name things removes functionality.

In the following case:

     //B1 is renamed as first
     //B2 is renamed as second 
     _______________
      f(x)| C3 = first * second
     _______________
       A | B | C | D
      _______________
    1|___|_2_|___|__
    2|___|_3_|___|__
    3|___|___|___|__
    4|   |   |   |  

vs

     _______________
      f(x)| C3 = B1 * B2
     _______________
       A | B | C | D
      _______________
    1|___|_2_|___|__
    2|___|_3_|___|__
    3|___|___|___|__
    4|   |   |   |  

It barely matters if you copy paste the first one or second one into a new sheet. C3 will be pointing to null. If anything its easy to trouble shoot former because you can chose any cell in the spreadsheet and call it 'first', chose another and call it 'second'- Compared to say to having fixed cells B1 for first and B2 for last.