I want to clarify my vocabulary first, there are two kinds of tutorials. There is the introduction tutorial where the player learns the basics of a game, and in depth tutorials for advanced topics. I am talking about the former -- only the situation of tutorials for new and inexperienced players of the game.
The general function of the starting game tutorials are introductions
to common gameplay elements that makes the game playable to the player. Your player's short term memory only has enough slots for 5-9 memory primitives*. And I mean primitive. A single digit takes up one short term memory slot. This might be why US phone numbers are 7 digits long. Going too in depth and doing too much too soon will cause more problems for the player. I also have a study sitting around somewhere that found that going too in depth results in greater appreciation for the complexity of a topic, but the person becomes more disinterested in perusing it.
The critical point for any tutorial is the player being able to identify what they are doing wrong and then modify their behavior accordingly. That is the beauty of pedagogical techniques like I do (teacher demonstrates) you do (student does it on their own) we do (student and teacher do it together, here mistakes can be identified and corrections can be made). Some of these will be trivial like moving the player avatar, to something that would be a bit more specific to the game such as repairing a hull breach. The repetition is also how something is committed to memory which frees up short term memory for new tasks.
Another issue is that different players will begin at different levels so the tutorial needs to differentiate instruction to match the needs of the player. I don't need to be taught wasd but someone else might. Everyone will need to be taught how to navigate their ship to another planet. And some players who are well versed in gaming or with good reasoning abilities might want to jump right in. I didn't read the civ 2 manual when I first got the game. My husband combs through any and all manuals and tutorials very carefully before even installing**.
If we are asking players to learn a lot of skills for basic, functional gameplay, especially those that are not common tropes or are different than what one might expect, then we must be really mindful of how the game is introduced to players.
The nice thing about separate tutorials is that they are easy to write and code for. The problem is they are lousy at their job.
*Except teenage girls. The memory area of the brain is powered by estrogen, resulting in young women to be able to hold up to 15 items in short term memory. This is also why teenage girls will remember every way you have wronged them.
**Thankfully I broke him of this habit
I also suggest taking a look at studies of the
tutorial for the first Super Mario Brother's Game for NES.