It’s usually obvious when you add or remove an effect such as distortion or compression — an effect that affects a track’s or channel’s volume — you’ll also need to adjust the track’s or channel’s volume fader to keep your mix in balance.
But less obvious is that when you add other types of more subtle effects, even if the level of the track or channel seems the same, you may need to go back and re-check the mix balance. The context of the effected signal determines what happens to the overall mix as you add the effect or processing.
It’s not unusual for just a little EQ or a slight amount of modulation to change the balance or apparent balance of your mix. This might require you to re-balance other tracks to give space to or to compensate for the newly effected signal. For example, you may want to add a slight EQ tweak or a slight slap delay effect to a bass guitar, but that may mask the kick or toms to some degree, requiring mix adjustments.
So whether it’s obvious or not, after you add processing to a channel or track, take a step back, re-listen to the mix, and re-balance as appropriate.