When spreading or manipulating data, you can temporarily lock cells while Planning calculates and fills in other values. You can visually review the changes before saving them. See Examples of Spreading Data with Cell Locking.
To temporarily lock values:
Select the cells to lock.
Select Edit, and then Lock/Unlock Cells or enter Ctrl+K.
A tan background indicates that a cell is locked. If you lock multiple cells, some of which are already locked, all the unlocked cells become locked.