When an Excel file contains many Excel data links it might start to scroll very slowly, taking very long to update and feeling very unresponsive. When opening the Task Manager, you can possibly observe that Excel takes up most of the CPU time.
Excel includes a mechanism that notifies the user of possible error causes in a worksheet. The automatic error checking mechanism causes Excel to update all Excel data links whenever a single cell is marked as containing an error.
Disable the automatic error checking mechanism in Excel: