Freedom from overflow, and noise floor stays level-dependent. Meaning that when you multiply your float signal by a certain volume the quantization noise is at

Freedom from overflow, and noise floor stays level-dependent. Meaning that when you multiply your float signal by a certain volume the quantization noise is at most -140 dB RMS. If it were integer, the quantization noise would depend upon how loud your (signal x gain) is. Besides, top-level compressor/reverbs use double :)