Quantities in Context
One of the differences between physics and mathematics is that mathematicians don’t tend to care about the units they are working with. In fact, they will usually consider all quantities as unitless^{1}. This makes it easy to compare quantities, because one only has to look at the number itself. If you have two numbers, 5 and 9, you know that 9 is the larger quantity.

Actually, theoretical physicists like to do this too, since everyone agrees that dealing with units can be annoying. This is why you might see physicists saying that the speed of light is c=1. ↩