to clarify:
make -j == use all available cores to parallel compile.
make -j4 == use 4 cores to parallel compile.
If you have a 4 core CPU or more you can specify using -j8, -j6 etc, but 99.9% of the common use case is do not specify the number of cores.
The make all is from earlier Makefile’s when we didn’t rebuild it. Today running make implies make all
To conclude:
use: make -j
for the fastest build time using the maximum number of available cores on your system.
Personally: make clean; make -j