Would you give your bank account number to a stranger?
Would you give your credit card numbers to a stranger?
Then why would you allow a “stranger” access to your computer and all of the personal information that you have?
A common scam these days is that you see a message on your computer that says you have malware, and to call a phone number to resolve. So you call the number and you speak to a “Microsoft” technician who asks to take over your computer and analyze what is going on. You do, and of course he finds tons of errors that result in your computer, cell phone, and other devices being compromised, and for the low price of $299 or $399, he will resolve all the issues on your computer.
First, if you see this type of message, you do, indeed, have malware on your computer. It is the person at the end of the phone number that put it on in the first place. Second, these people are not from Microsoft, but from some shady tech support company that claims to be partnered with Microsoft. Third, when you give permission for the tech to get on your computer, he can access any data on it, hide or delete files, or change your password so you cannot get on your computer if you do not pay him to fix it.
The same is true for random calls from “Microsoft” to you, saying that they have monitored your computer and want to show you problems.
The fourth possibility is that you call some tech support and get a scam person instead.
Bottom line: If someone wants to get on your computer and look around, DO NOT LET THEM!