"Guard position" is a conflation of the topics of distance awareness, proper position to close a line, and framing. Beginners lack all of these skills, and it makes sense to teach them together. Not being aware of the time and distance an attack requires, they need to keep their best possible guard at all time. The small variations between large, medium, and close distance are hard to determine, and vary for each individual. However, as skill increases, gradations need to enter in. There is conflict between readiness and giving the opponent knowledge of your defensive intentions. Ideally, no defense would be presented until the last possible moment, to deny the opponent the ability to react or plan a compound attack. There are many difficulties with this, including reaction time, variable speed attacks, and ability to read the opponents target. Stepping back from that, presenting a guard only as you enter medium distance serves as a framing device, limiting and prompting the opponent's options. Another step down is to maintain a guard in medium distance. Maintaining distance gives the opponent time to think- whenever possible the distance should be closed immediately or only for chosen windows of opportunity.
A strong tactical path should constantly improve your position until you win. The stronger the path is, the longer it could be. So a weak path goes maybe one tempo, "I am in distance, the target is open, I hit you", while a stronger path would start from out of distance. The infinitely strong path would start something like, "I woke up this morning."