Compiling programs is usually one of the cases that does benefit from filling all the hyperthreads, though? That's why people often cargo cult running "make -j<cores * 2>".
In case other people don't see why this would be the case, hyperthreads are good for running a second thread while the first one stalls while waiting for something such as a memory read. Compilers often work with indirect data structures such as irregular graphs and symbol tables which don't cache perfectly and may cause memory stalls.
