Dynamics processors are essential when recording, mixing and editing music. But when it comes to compressing an entire sum signal, a lot of digital compressors turn out to be unusable, many of them were made to process single-track signals only.
On complex sources they tend to produce a ‘pumping’ sound, distort or just make your music lifeless. There are manufacturers telling you ‘this is the only compressor you’ll ever need’. Don’t believe them. Sound signals are far too complex to be handled by a single device.