This is for removing / doing up the valve core. If you don't have a tool for it, #11 on the spoke tool fits nicely. Yes, I will buy some of those cheap doo daddies - never had a need for one till now.
bicycles don't use 11g spokes. Motorcycles do.
Pretty much every Emtb will come with 14g (2.0mm spokes) 3.3mm nipple flats.
Ooccasionally if you're a weightweenie 15g (1.8mm spokes) 3.23mm nipple flats.
Cheap bikes and old shitters often use crappy 13g (2.3mm spokes) 3.45mm nipple flats.
so most of the spoke key sizes on those cheap multi spoke keys are actually completely useless for bicycle spokes.
But cool you've found an alternate use for it.
a removable presta valve core has 4mm flats and if I don't happen to have a valve removal tool a small andjustable spanner is usually my first go to tool for removing them. Longnose pliers will also work if you have nothing else to hand.
Quite a few bicycle multi tools have valve core removal key next to the spoke key(s)