Knowledge of how much wattage is needed for a venue relevant to the number of attendees is of great importance for live gig set-ups. You can either overpower or underpower your speakers if unaware of such details.
Now that you have the right voltage, wattage, matched amps or active speakers where the ohm rating is a perfectly sealed match, we go to frequency response which is a necessary detail before you calibrate your cross-overs and equalizers. Think of it this way - you canˊt put a pitcher of water into a small glass. You will just spill the water, make a mess and waste it. In audio language, you must not feed any frequncies which are beyond the speakersˊ frequency response. For example, monitor speakers with an effective frequency response of 100hz to 19khz should not be fed with 60hz signals. It will just cause noise and ruin your whole mix. Knowing the speakersˊ frequency response and feeding what to which speaker is the key.
Surprisingly, there are a lot of sound engineers who will just jump into calibration and mixing of a system without even knowing the details of the speakers which is a big mistake.
By knowing your speakers well, not only do you protect your equipment but you are also guaranteed of a better mixing experience and quality sound.
Summary tip of the day: Know the technical specs of your speakers before doing anything; and that means everything.