So there's a little 'trick' I use when I am fighting another Zerg and I get into a muta vs. muta battle. To help ensure I win the battle, I'll run my lings underneath the battle.
What this does is make the glaives bounce to the lings sometimes, giving me an edge in terms of effective damage.
I never notice people doing this when I watch games. Is it because they want to be doing other stuff/covering other areas with the lings? 'cause testing in my unit tester, 40 mutas v 40 mutas the results are fairly even every time, the winning side usually not having more than 5 mutas left. When I park some lings under one side, however, that side wins pretty distinctly every time, with ~15 mutas left. I even gave the other side an armor upgrade and the side with the lings still won quite handily.
Of course 40 mutas is quite a lot, but it demonstrates that this technique can be quite effective in reducing your muta damage taken.
On Googling it appears that people do do this, but I just never see it or maybe never notice it? I dunno.