(except beer by the tap which has to be imperial)
heh. In Portugal, "imperial" is what you call beer by the tap
(though maybe it refers only to the half-pint and/or pint, I don't remember
I like (or not) how there's a difference between "US" and "imperial" volumes which all differ by a factor of 0.832 (ie: google tells me 1 US gallon = 0.83 Imperial gallon), except for the ounce, which is 4% smaller in the US...
edit:
Having that said, the few prefixes outside the "1000-fold" raster are essentially for old units of measurement (UOMs)
except Centi- (and deci- but less so) that are pretty useful for volumes and distances: the standard wine-bottle is 75cl, and cooking is also mostly in cl and liters; and people usually measure things in cm unless they want to get precise
also, an hectare (ha) is 10'000m
2 (so, like 1 square hectometer if you want the SI prefix). As Job said, you'll use it for fields, or any types of land-surface that's between a house and a city in size.
as for Deca- you might find "decameter", but rarely (last time I saw it was in PE, when we used 10- or 20-meter stripes to see how far we could throw things). That and the runways is pretty much all the use you'll have for it