You can create and use whatever units you wish - QB doesn't know what a gram or ounce is - you have to tell it all the units you use and define the factors between units - therefore you can also makeup your own units if you use something special in your business or trade. Cases, masterpacks, and pallet packs can be created for wholesale/retail merchants.

The general advice for working with UoM is to use the smallest unit you want to define as the 'base' and then make all the other units larger multiples. That might not be ideal if you normally work in kilos, but occassionally use a gram. 

If you do define alternate units that are less than the 'base' then try to ensure there is an exact decimal multiple between them. ie: don't create a sub-unit that is 1/3 of the base (0.33) - it can cause rounding errors.