Picture a budget holder filling in your template. Somewhere in there they type "none" into a cell that's meant to hold a number, or they pop next year's headcount into the salaries row. Then they submit, feel productive, and move on.
A few days later the reviewer finds it. Now the submission has to go back - except the budget holder has long since forgotten what they were thinking, the reviewer has lost half an hour, and the whole thing limps round for another lap.
Which is fine, in the sense that the error got caught. But it's a bad way to catch it.
The cheaper error is the one they weren't able to make. That's what data validation is for - building the guard rails into the template itself, so the wrong thing simply can't go in. A cell that won't accept text where it needs a number. A dropdown instead of a free-text box, so nobody invents their own spelling of a cost centre. A check that flags a line red when it doesn't add up, or refuses to save until it does.
Excel is totally brilliant at data validation and it's criminally underused.
Anything validation can catch, it should catch. Every error you stop at the point of entry is one that never reaches the reviewer - and reviewers are your scarce, expensive resource, and shouldn't look at problems a dropdown could have prevented. There's an old quality rule of thumb that a mistake costs a pound to prevent, ten to catch later, and a hundred once it's baked into a decision. Finance is no different.
The trick is not to get carried away. You don't validate everything - do that and you turn the template into a huge pain, and people either give up or find a way around you. Validate the material numbers, the big ones that move the total and the ones that are painful to resolve later. Leave the judgement calls to the review, because that's the bit a human is actually needed for. Validation handles the mechanical; review handles the thinking.
So before you do another planning cycle, have a look at your review checklist. Half the things on that list shouldn't be possible in the first place!
