I am currently studying music theory via https://mymusictheory.com and I can't perhaps understand the English this teacher is using while trying to explain these two rules of adding rests:
If the rest you need is worth less than one beat, use smaller rests to complete the beat or sub-beat, before you do anything else.
When completing a beat or a sub-beat, always put a larger note/rest before a shorter one, and not the other way around.
So for the fist rule, I believe it would have been sufficient to say: "use rests to complete the beat, before you do anything else." since we know that the rests we need have to be less than one beat in order to complete an incomplete beat.
Is it also necessary to say "beat or sub-beat"? Isn't it suffice to pick "beat" or "sub-beat" and just say one of them since they both serve the same purpose here? I think the teacher is using completing a beat equally to completing a sub-beat. Because what is the purpose of completing a sub-beat (in its literal sense) as it doesn't add to the neatness of the bar. Or perhaps I've got it wrong somehow..
For the second rule (and to further clarify) the first rule, I'm going to have to go with examples (this is a screenshot):
So in Example e. we need to have a 16th rest after the 16th note in order for it to be a complete beat? In Example f. we incorrectly find a longer rest after a shorter one but, in its current position, won't that quaver note + shorter rest equal a dotted crotchet? Isn't two dotted crotchets a fine way to organize bar f? Perhaps it's only necessary to complete the smaller "beat" when dealing with compound time.. And in Example e. we could argue that the dotted crotchet being at the end of the bar is wrong, no?