It’s really common sense and you may get away with not doing this at times. But to get your mic preamp at it’s best level, remove or bypass any gain changing devices in the signal path.
If you have anything in line, you don’t really know what level your preamp is giving you. For example, if the compressor is in the path and it’s input or output is low, the level at the DAW may look fine, but you may hear distortion because the preamp is too high. Remove the compressor and BAM! You find the levels are in the red. The reverse, preamp low, compressor output way up, can result in a noisy signal. So remove or bypass anything in the path when setting levels.