About the different applications of audio delay effects.
There are quite a number of different types and applications for the audio delay effect in the audio production ranging from plain technical delay application up to all the musical and creative ranges of application. The rather technical or correctional delay typically is a plain digital delay which serves as a sample accurate alignment tool. Such alignments might be necessary for example for plug-in delay compensation (when a plug-in introduces latency) or during the mixing process to align a group of recorded tracks or samples. The so-called pre-delay can also be seen as an alignment sort of thing where the direct source signal has to be aligned in a positive or negative manner in relation to a processed signal, e.g. in a reverb effect.
Creating ambience and echo effects in a mix is another and important domain of delay effects. The simplest one is the single slapback echo effect which already can create a sort of depth or width impression without utilizing any sophisticated reverb. Further repeats can be obtained either by adding further delay lines or by introducing feedback loops in a circuit which already can create convincing ambience and reverb effects as long as the perceived density is high enough. If an improved depth perception is the goal then its important to attenuate the delayed signals high frequency content. In a busy mix this might even perform better than a super dense and sophisticated reverb.
The delay is also an excellent groove tool. If the timing of the delay is synced to the songs tempo the door is open to create rhythm oriented repeats and full patterns. Using triplets and dotted notes or even combinations might be a valid groove foundation but losing the absolute timing precision might be the ticket if getting the groove right is the task. Introducing filter and modulation effects to a delay line opens the door to a whole range of creative delay effect applications. Splitting the spectrum for different delay lines or decompose a signal in a delay network can lead to a complete deconstruction of the original sound.
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Variety Of Sound 
A thing that I tend to do with delay for a mono source is have a single tap delay, somewhere between 3 and 30 ms and invert the phase of one side of the delayed signal. This gives loads of stereo width, has comb filtering that boosts frequencies on one side but attenuates them on the other, and completely cancels in mono leaving the original signal unaltered. It’s kind of an invisible way of adding space/width without actually being able to tell how the space was added.
great tip!
Actually got the idea from here:
http://www.recordinginstitute.com/da154/ARP/chap3Sig/0305delsh.html
Scroll down to “stereo effects with combs”
I wrote a reaper JS effect to do it quickly without having to set up any routing, and including a LP/HP filter for the delayed signal: http://dl.dropbox.com/u/22634122/Haas
Love that tip. Thanks
Thank you!