I'm sure for real sound guys its no biggie... but just getting the delay right with those speaker stacks would be so important.
In my very mild reading on pro-sound spaces, the big guys seem to really like L'Acoustics.
It's not that difficult. You could even do it by ear if you know what to listen for. If you're ever playing a large room where the level of sound at the front of the dance floor would be noticeably louder or more uncomfortable than the sound further back, then you should be using delay speakers (or linear array) if possible. It's this "boom" affect the column arrays will tend to reduce by dispersing the energy across an expanded vertical field. (i.e. a linear dozen 3" speakers versus a single 12" or 15" direct radiator.)
Keep in mind, that these linear column speakers are not line arrays, rather they use the vertical stack to resolve coverage issues in the vertical plane. If you listen to the classic pair of 2-way boxes on sticks that came to define the mobile DJ - you can soon find some serious limits with the vertical coverage. Even without being aware of the issue - people will reflexively resolve the issue using speaker stands to get the mids and highs to a workable plane.
Linear column speakers have a trait in common with actual line arrays which is a fixed horizontal dispersion. So, as you look at the picture earlier in this thread the number of these column systems used in the audience is based on that horizontal dispersion angle. The delays are a function of the power profile and the desired sound pressure levels across the audience.
Linear columns and Linear arrays differ with respect to how they deal with vertical dispersion. The column speaker has a uniform power profile and uses multiple inline drivers to expand the range of vertical dispersion. A line array has specifically targeted elements that are literally aimed at a given space, and the power level of those elements may differ given the distance to their target. In addition, you largely won't hear (or hear a greatly diminished) sound from elements of the array not targeted to your seating position, so the sound appears uniform as you move through the sound field. If you turn off a given array element and walk from rear to front of the sound field you will literally experience an easily recognized dead spot where that element is supposed to deliver. They can be that accurate.
L'Acoustics stuff is amazing. I've worked with their Kara line arrays both flown and on sticks and the coverage is amazing. The alignment is pre-configured for each situation using computer software, so it's really about either having or predicting an accurate representation of the sound field. L'Acoustics arrays like these:
Buy L'Acoustics are obviously for touring and large venues, but they and some smaller and lighter versions like the KIVA can also be great for smaller gigs.
Either can be used as small arrays on stands or discreet fills to achieve really great coverage and uniformity. The speaker lying on the front corner of the stage in the picture below is a Kiva (one of a pair) being used for front fill at a dinner event. 2 other pairs on stands provided the mains (with subs) and single Kivas on stands delivered the delays further down the ballroom.
