As above, Corby.
I can recall twenty years or more ago when I had a very large spreadsheet, when making new entries the recalculation would take quite a few seconds (the entire spreadsheet is recalculated, not just the formulae affected by the new entries). This could be very time consuming if you had a large number of new entries to make. More than that, if you did an automatic import of new data it could on occasions cause the entire spreadsheet to lock up. The answer was to set the calculation to manual and then do a recalculation after all the new entries had been made.