It doesn't matter if it's a proprietary format. Proprietary formats can be reverse engineered and modified and converted. There is a world of difference between

It doesn't matter if it's a proprietary format. Proprietary formats can be reverse engineered and modified and converted. There is a world of difference between a proprietary file that I have online in a form that I can't access directly (and I have no idea how it's being accessed, changed or stored by the service itself or third parties) and a file that I have on my harddrive that I have complete control over.