V4: How does half numbers work for spacing?

[NielsKlop]

In V3 you had values for size and margin and padding like 1.5 and 2.5. I noticed I can still use .5 with any number in V4 so I could use 10.5, but it still has be only .5 so I can't use things like 10.4 or 10.6 is there a reason for this? Also I don't see any documentation in V4 about even the ability to use .5 as a value.