Well... from what I read on skill development a lot of it says that repetition of a correct form is the key to developing the muscle memory that allows us to make a repeatable shot under stress (I don't think muscle memory is the "in" word for it now though).
I have the attention span of a young cocker spaniel, so tend to shoot groups of arrows in small numbers just so I can maintain focus. For me... it seems like if I am trying to work on something (part of my form, release, follow-through or whatever), I am better served by shooting a group to see if my adjustments are bearing fruit.
I know that in the other shooting disciplines that I do, constant repetition with good focus is the key. Pounding it shot, after shot, after shot on one target presentation CORRECTLY gets me where I don't really have to make a conscious thought on how to make the shot when in competition (or a hunting situation). I also work on WHEN to hard focus as well (again, more valuable in my other shooting disciplines than in my archery perhaps). I think I read somewhere that we can only truly hard focus for about one and half seconds and training might be able to improve that to three.
I like shooting one arrow at a time from different distances and angles but it's a different kind of practice I think than concentrating on shooting form and such. I guess it comes down to what is good practice for each individual or what it is you are trying to improve with the practicing.
OkKeith