Add a second "Locked" option for cells, which only allows data entry and deletion when a sheet is protected.
When you have cells which have to remain unlocked for user data entry, and formulas that rely on the data from those cells, it can break the entire sheet when someone accidentally performs a drag-and-drop/cut-and-copy. You can only hope that it’s broken in a way that is glaringly obvious, so that it's caught.
It would be nice to be able to have a second tier "Locked" option, perhaps called something like "Data Only". It would be a third check box, alongside "Locked" & "Hidden", when formatting cell protection. It would limit cell interaction to entering and deleting user data.
It is unbelievably frustrating when you spend 100+ hrs, developing a quote calculator, only to find out that, even though the sheets are locked & password protected, your entire workbook ends up broken due to someone accidentally dragging one cell that has dependent formulas onto another cell that had dependent formulas.
Yes, it's easy to undo the action, but when you have to release a workbook like this, and you have to be able to guarantee that all users will get the exact same results 100% of the time, it leaves an uneasy feeling in the pit of your stomach. There are plenty of oblivious people that may not even realize that it’s messed up. It's possible that someone could unknowingly be giving customers bad pricing, which can cause you not to be awarded business due to overpricing, or to lose money on underpriced jobs.