The main difference between the two is the opening and closing mechanism. While you open the bows of a folder with a lever mechanism, ring binders have a tear mechanism. You open them by pulling the rings.
Ring binders are usually narrower than folders and are therefore more suitable for travelling. The lever mechanism of the binders, on the other hand, makes it easier for you to file and remove documents.

Often you will find information about the spine height on the manufacturer's pages, but not about the
about the capacity of the folder. This is based on the actual filling height, which corresponds to the distance between the top edge of the metal rail and the bottom edge of the loop. 100 sheets of paper with a thickness of 80 grams per square meter result in a stack with a height of eleven millimeters. So you can calculate the capacity based on the filling height.
Simple rule of thumb for orientation: a folder with a spine width of eight centimetres holds about 600 sheets, a narrower version with five centimetres just under 350 sheets. Dividers, tabs and thicker paper take up more space and reduce the capacity.

As a private person, you are obliged to keep official documents, such as
birth and marriage certificates, for a lifetime. Otherwise, there are no fixed retention obligations. However, you should have certificates, insurance documents, contracts, proof of income as well as bank statements for the last four years and relevant tax documents at hand in case you are required to provide proof.
Business documents are a different matter. A business must be able to produce various documents in the event of an audit. The retention periods range from six to ten years, depending on the type of document.