A question worth answering before it happens, not after.
If your files only live on that one laptop, the honest answer is: you could lose all of it. Customer details, invoices, years of records — gone, along with the machine. Most business owners assume this won't happen to them, right up until it does.
Your files saved in a second, safe place automatically — no remembering to do it yourself.
A backup checked to make sure it actually restores a file, not just assumed to be working.
Devices set up so a lost or stolen laptop can't be opened by whoever finds it.
A clear, simple way to get back up and running on a replacement device, without losing days.
None of this needs to be complicated or expensive. Set up properly once, it runs quietly in the background — so if the worst happens, it's a mild inconvenience instead of a disaster.