This subject is especially important in the sword arts, because of the tools we use in practice. Punching your neighbour accidentally in the face may draw swift retaliation, but most likely, someone will end up with only a couple of bruises. On the other hand, an errant swing from an Iaito, to say nothing about a shinken, has much more dire consequences. That is why it's so important to stagger.
|A typical arrangement for seminars|
While it is everyone's responsibility to ensure they have adequate space to train, when the lines begin to form (typically ordered by rank), the seniors should naturally be most accountable. In fact, I believe there are three individuals that are key to the arrangement of students in the dojo. Let's call them Atsuki, Baby, and Cutey - or A, B, and C.
A's role is to establish the forward space limitations - keeping in mind the distance from the instructing Sensei and observers, as well as any physical objects that could be damaging or damaged. A should keep in mind ALL the possible kata that the group will be performing, and be flexible to adjust these limits if more space is necessary. Ex. Moving the line back for Seitei-gata #11: Sou Giri
B's role is to create the standard horizontal space limits between students in the same row. Too close, and you risk hitting A (or A's sword) during techniques like Seitei-gata #7: Sanpo Giri's side cuts. Too far, and you crowd out the juniors on the far side of the dojo/gym.
C's role is arguably the most crucial, because they're chosen spot determines both horizontal and vertical spacing. If he/she doesn't stagger properly, everyone from rows 2 and up are forced into unbalanced and unsafe positions.
Here's what it an ideal line-up will look like - Recall line #3 should be behind line #1, and line #4 behind line #2:
So next time you are lining up, take note of your responsibility. Everyone to the front and right (or more senior) is your guide; while everyone behind and to the left (or more junior) are your responsibility. Good Luck!