The basic idea is that modes make the same action (pressing the "D" key, for example) do different things. They make things easier for programmers who want many operations on machines that only have a few possible actions, but they make things hard for the user who have to pay attention to the current mode and know how to navigate from that to the mode where the desired operation is possible.
The basic idea is that modes make the same action (pressing the "D" key, for example) do different things. They make things easier for programmers who want many operations on machines that only have a few possible actions, but they make things hard for the user who have to pay attention to the current mode and know how to navigate from that to the mode where the desired operation is possible.