Sometimes this advice of describing what something is and why you'd use it is helpful. Other times I already know what it's for and just want to use it, and don't like having to slog through descriptions that don't help with implementation. There is no universal right or wrong answer here, since it will depend on who is reading your tutorial, what their level of expertise is, and what they need.
A tutorial can provide the best of both worlds by putting the background stuff of each section in a sidebar, so the reader can easily skip it or delve more deeply if they wish.
Sometimes this advice of describing what something is and why you'd use it is helpful. Other times I already know what it's for and just want to use it, and don't like having to slog through descriptions that don't help with implementation. There is no universal right or wrong answer here, since it will depend on who is reading your tutorial, what their level of expertise is, and what they need.
A tutorial can provide the best of both worlds by putting the background stuff of each section in a sidebar, so the reader can easily skip it or delve more deeply if they wish.