So many developers are adding various convenience macros to the
Prefix.pch is a precompiled header. Precompiled headers were invented to make compiling faster. Rather than parsing the same header files over and over, these files get parsed once, ahead of time.
In Xcode, you add imports of the header files you want in a “prefix header,” and enabling
Precompile Prefix Header so they get precompiled. But the idea behind a prefix header is different from precompiling.
A prefix header is implicitly included at the start of every source file. It’s like each source file adds
at the top of the file, before anything else.
You can remove the precompiled header. This question has been already answered in thread I'm linking below. It contains all the information you need as well as useful comments.