Your data is not yours. This means the Online version is for folk that want ease of use above all.
But it's not secure against your government and ISP meddling. Here's a fellow you may know on this subject:
So while it has it's proponents, if you care about your data, you don't have it only in the cloud.
Let’s start with a simple comparison between QuickBooks Desktop vs online. Usually, they are totally different products and they are fit for the different requirements too.