Comment # 14 on bug 1182252 from Jan Engelhardt

One case is that `pkg-config xyz --libs` (or older xyz-config --libs) sometimes
emit, due to xyz developer error/lazyness, extraneous -l options that should
only be emitted when --static is in use.

Another case is that xyz is a library with inline functions, which may warrant
adding -l to .pc files at all times because you can't know whether or not a
xyz-using source actually included the particular inline function.

That would be two casess I can think of why openSUSE, and relatedly Debian, use
--as-needed.