Insert inputs and outputs on an audio console are very useful for adding audio processing--like parametric equalization, delay, reverb, etc.--that are not available on the console.
Insert points, when they are provided, are typically located on each channel strip, and on some consoles may also be available in some of the output strips, like the groups. For an analog console, insert points can be balanced or unbalanced, and this is something to check when looking for an audio console. Also check the insert output level and the expected insert input level. It may be standard operating level (usually +4 dBu) on consoles with balanced insert input/outputs, but it could be lower. 0 dBu is not an uncommon level for insert points.
For unbalanced insert points, the level will more than likely be lower than standard operating level. Which to choose?
Balanced circuits are more immune to noise, and that's a big plus; especially if you use insert points on many channels simultaneously. Unbalanced circuits by their nature will be noisier. If unbalanced connections are short and kept away from electromagnetic interference (like power lines, power transformers on equipment), you can get useable results on a single channel. But remember noise will add as you use more than one insert point at the same time.
Cost is another consideration. Many lower cost consoles use unbalanced inserts even though they may have balanced channel inputs and buss outputs.
See what type of connections your processing gear has. If they are different from those on the audio console, you'll need interfaces to go from balanced-to-unbalanced (and vice versa). These are extra cost items that take up more rack space.
