You should encrypt files or folders when you think it is important that they have the strongest protection that Windows can provide. Because encrypting files and folders is easy, you might be tempted to encrypt all of your information. You can do that, but there are some things to keep in mind:
You need to make sure that you back up your encryption certificate and encryption key, and store them in a safe place. If your encryption certificate and key are lost or damaged, you won't be able to use the files that you have encrypted. For more information, see Back up Encrypting File System (EFS) certificate.
If you encrypt a folder, any files that you create in that folder will be automatically encrypted.
Other people who want access to files or folders that you encrypt must have their own Encryption File System (EFS) certificate added to the files. With this certificate, they can access the encrypted files or folders when they are working on your computer. If the files are shared, they can access them from another computer running Windows.
If you copy or move a file to a computer or volume that does not use the NTFS file system, the file will be decrypted.