We have tested sites up to 1 gb on low level server and 2 gb at dedicated server, backup depends on your server configuration. The limit completely reply on your server. We have made process to run on almost at any server. But click here to read more about backup requirement.if you have very large site you can use exclude directory option to omit unwanted folders.
Here is the test results screenshot
We will update with more screenshots as soon we get latest test results.