hello XLers

I have a general question about best practice in Excel . My workbook has
about 40 sheets. On each sheet, there is a very lengthy formula dragged
over a range of about 120 cells. Everything works fine, but it occurs to me
that this long formula is repeated 4800 times, making the file kind of big.

Is it better practice to use code to populate the cells with formulas, say
when a sheet is activated? Should I then depopulate the cell's formulas
when the sheet closes? Is it better to use code to populate the cells with
values calculated in code, rather than write the formulas to the cells? Are
there speed issues?

Any comments are appreciated
anny