Limiters are used to control transients and increase the overall level of a recording. The average level of mastered recordings has been increasing since the 1980's. This trend is often referred to as the loudness wars. In order for modern pop recordings to meet acceptable commerical standards digital peak limiting must be used in mastering.
De-essers are most often used to control high frequency peaks found in a vocal performance. These peaks, known as sibilance, occur when singers use consonant sounds like "s" and "t." Siblance sounds unpleasant, harsh, and needs to be controlled. For this, we typically use a frequency dependant compressor, also known as a de-esser.
Mixing in mono has become a popular topic of discussion. Some noted engineers do the majority of their listening in mono. This practice may seem strange. However, there are benefits to previewing your mix in mono.
Listeners using small devices will hear a mono presentation. Often times clubs or venues use a mono speaker system. EDM production must be compatible with this listening environment. For these reasons, it is important to know how your mix will translate to mono.