Different behavior of apply!(K,ch) compared to apply!(K,f,ch)

I wanted to create different functions for setting up the system matrix and setting up the load vector.
So, I thought I could do `apply!(K,ch)` for the system matrix and `apply!(f,ch)` for the load vector separately.
Obviously that only works if there would be no contribution to the right-hand-side when applying the conditions to the system matrix.
However, I didn't think much about it and it took a while to figure out that `apply!(K,ch)` is not doing what I expected.
My question now would be: When would `apply!(K,ch)` actually be used?
And would it make sense to give a warning, when using it or explain the differences in the manual?
(Just so the next person making the same mistake as I did does not take as long to realize.)