All cells on a worksheet are "Locked" by default. When you apply Protection
to the sheet, with or without a password, you can no longer make changes to
Locked cells.
So begin by selecting and using Format --> Cells --> Protection to "Unlock"
the cells you DO want to be able to make changes to, as in deleting some user
input. Leave the ones with formulas in them locked. Then apply Protection
to the sheet.
You can select more than one cell at a time to unlock, but I usually make a
boo-boo somewhere, so I'll grab a few at a time and unlock them and then
choose some more and repeat until I'm all done. You can also choose entire
rows or columns to unlock/lock.
