Actually, I believe that Names, in and of themselves do not speed formula exicution.

If =myValue is in A1 and =myValue+1 is in A2, the name myValue is calculated twice, once for A1 and once for A2.

Otherwise, names with relative referencing would not calculate correctly.
(e.g. Name: myValue RefersTo = COUNTA(Sheet1!$B1:$D1) (note the relative row referencing))