I've been thinking about the way most OS's handle scrollbars. The general pattern is an invisible scrollbar that only appears when the user scrolls. This is the case on Mac OS, iOS and Android (see image below).
Is this a good pattern for UX?
In my opinion it is very important for users to know that you can scroll. Without this users might miss important content, grow frustrated and fail to complete user tasks.
I was wondering what your opinion on this is and if there's research that supports either way of handling scrollbars in UI/UX?
My own findings
Apple specifically states the behaviour of scrollbars in the iOS Human Interface Guidelines.
A scroll view itself has no appearance, but does display transient scrolling indicators as people interact with it.
Source: iOS Human Interface Guidelines
Material Design (Scrolling Techniques) describes a lot about scrolling behaviour but nothing about scrollbars. Some Android OS applications do not have scrollbars at all.
I see what the pros are. It saves space and looks good. However, there are some cons, too. For a user it is less clear that there is content below the fold. You can help the user by having content being cut off from the fold (see below), but that is not always enough.
Apple has an option in Mac OS to make scrollbars always visible, but not in iOS.
Windows uses scrollbars that are always visible.