[1] Particularly when you have to say something which is almost, but not quite right, and because you're writing an academic paper, you're both worried that a reviewer will dock you for being so naive, and as an academic it pains you to say something which is not technically correct, but you have this pesky 10 page limit, so you stuff the pedantry in scriptsize font on the bottom of the page.
Eh, don't ever say things that aren't correct. It's not wrong to say that something is a way of approximating or whatever; use your linguistic qualifiers. If you need more space, ask for it, or say less and write a second essay/article/whatever.
Footnotes are much better used for pointing people to further reading material.
[1] Particularly when you have to say something which is almost, but not quite right, and because you're writing an academic paper, you're both worried that a reviewer will dock you for being so naive, and as an academic it pains you to say something which is not technically correct, but you have this pesky 10 page limit, so you stuff the pedantry in scriptsize font on the bottom of the page.