Treatment of registry entries in connection with file associations

I have already pointed out in another thread to this topic (see on the end of my comment with the subject "research incompletely"). As I suspect, however, that this problem was not noticed sufficiently, I've decided to create this new thread.

Suppose a base app creates in connection with a file association in the registry the following entry:

HKLM\SOFTWARE\Classes\.xyz

At first I assumed that I must make the following entry in the section [RegistryKeys]:

-=HKLM\SOFTWARE\Classes\.xyz

Then I discovered, however, that this code is unnecessary in the portable app Drago Portable.

My question now is, whether that above code in the section [RegistryKeys] is superfluous? Or is it different from case to case?