The way I use it, Chloe, the "practical note" is the opposite of the "theoretical note". I presume that the sentences before the sample you shared above were mentioning different points about uniforms and I would also guess that they were slightly "negative" points or ideas or arguments or theories about uniforms. Then the author decides to change it to something positive by mentioning the actual benefits of having to wear uniforms (actual and practical benefits as opposed to just ideas or theories). That's how I see it, anyway. Hope this helps.

To make a note, a comment, that is practical, ... To make a note, a comment, that is practical in nature, ... To make a note, a comment, on practical aspects, ... Now to comment on a practical aspect, ...

Chloe, the expression usually appears as a change-of-direction indicator, similar to "however" or "but". Do not try to interpret the phrase too literally.