Compression is a secondary tool for controlling and balancing your sources in the mix. It can reduce the dynamic range of a source, making it more consistent, punchy, or smooth. However, you should avoid over-compressing, as it can diminish the naturalness, expressiveness, or impact of the source. Generally speaking, use a low threshold and a high ratio to tame loud peaks and transients that can cause clipping, distortion, or feedback for sources with a lot of dynamic variation (e.g. drums, bass, brass). For sources needing more body and presence (e.g. vocals, guitars, strings), use a high threshold and a low ratio to smooth out the overall level and add some sustain and density. To catch and release peaks quickly without affecting the body and tail of the source (e.g. drums, percussion, plucked instruments), use a fast attack and fast release. For sources with smooth and long transients (e.g. vocals, wind instruments, bowed instruments), use a slow attack and slow release to let some of the peaks pass through while affecting the body and tail of the source. Finally, adjust make-up gain until the source sounds as loud as before but more even and controlled.