When a user needs help with a command-line-based application, they usually have two options for documentation: a website or the command-line manual, also called man pages.

Having to locate and read a web page in order to use an application could be considered a lot of hassle, which could deter new users of an application.

Similarly, the man pages within a terminal can be difficult to navigate. It is not intuitive how to search them for a specific keyword and the inability to scroll with a mouse can be offputting to some people.

Within most GUI applications, you will likely see a menu bar at the top. Inside this menu bar can often be found a Help option. This is a rather self-explanatory way for a user to locate instructions on how to use a particular application. The developer also has all of the tools to lay out this section of the application as they have for the main application itself, so they can enable things such as mouse scrolling and hyperlinks to make searching and navigating the help document very easy.

On the flip side of this, if an application has a huge number of different functions, translating this into a graphical interface can get very messy. There may simply be too many buttons and configuration choices to cram into a graphical window whilst retaining all possible features. Something like the Git version control system comes to mind here. Whilst graphical interfaces do exist, they can be much more complicated to use than simply memorizing the command-line options.