Booking the right opening DJs can be one of the hardest things to do, and depending on the size of the club or popularity of your event, it could potentially ruin your party from the very beginning. It is extremely difficult to book because they can be your free DJs who have little experience and little draw. That isn't to say they don't have a draw somewhere, but your particular crowd may not know much about them. You may want to give these new comers a chance to shine and build their name, but if they are not skilled yet, it can be a disaster. That isn't to say they have little value, but most of the time they are still learning. It is also hard to give the opening slot to DJs with a little more experience because most people hate that time slot and refuse to accept it unless they are doing you a favor. This makes it very hard to find someone that knows what they are doing, is willing to play for free or cheap, and is ok with the opening slot. This opening slot has such a bad reputation, but the reality is that it can be just as important, if not more important, than any other time slot.
If you are a smaller party on a Wednesday night, that holds 100 people and it's free, you absolutely have to have a solid opener. The reason being is that many people are already on the fence about even being out on a mid-week night, and if your event is free, they are less likely to care about walking out and going somewhere else, since they didn't pay. This can ruin your event because you need a certain amount of people to hit that "tipping point" where people start piling in, and staying.
Lots of times, if a DJ sucks on a smaller night, people will walk in for a minute or two, then walk right back out and find somewhere else because it is still early. This causes a detrimental domino effect. Now as time passes, and you've had 30 people (in groups of 2) walk in, then right back out, you are left with a dead dance floor where there should be 30 people. That's almost a third of what the club's capacity is.
The DJ may not even suck. Maybe they are just playing music that is not fitting the tone of the event, or the vibe of the crowd. We've all seen it before... The new DJ who is super excited to play for a crowd his first time, and thinks there is some sort of DJ scout judging whether or not he will be a superstar. This makes the DJ think he needs to play the heaviest most crazy dance music imaginable, to only 8 or 9 people. The truly talented DJ can diversify his sound to cater to the audience, especially if they are just easing into the night. How about this for an "ANALogy"... You wouldn't just power fuck your girl in the ass without some lube and easing into it slowly right? Well maybe if your girl is a super champion, but most likey NO. Same goes with the flow of a party.
Now it's 11pm and your next DJ comes on who is amazing, but the damage has already been done. Now the first thing people see when they walk in is an empty dance floor during what should be a peak hour. So what do they do? They walk right back out because they don't want to be at a dead party.
The music could be phenomenal , but there is a certain psychological discomfort associated with being at a dead party, and it causes people to want to escape. So if you want to set the right tone of your event, make sure you do your research, and make sure the DJ knows how to read the crowd, and can adjust to a mellower crowd that is just beginning to drink and "loosen" up.