In places such as Italy, one frequently finds them behind the high altar, shape in a semi-circle that aligns to the apsidal wall. (In the more northerly, gothically influneced parts of the world, they tended to be manifest in a linear fashion, found before the high altar within the chancel.)
These choirs were used either by clerics (sometimes by a chancel choir in certain parts of world) for the purporses of the communal recitation of the Divine Office and/or the participation in the liturgical and para-liturigcal life of the church in question. In the case of the Italian model, they tend to find their apex in a central prelatial throne.
To give you an example set within the context of the Italian tradition, here you can see the 17th-18th century choir stalls of the cathedral of San Alessandro Martire located in Bergamo which would have been used by the bishop and, more routinely, the canons and other clerics of the cathedral.
The episcopal throne with its kneeler |
Detail of the throne proper and the kneeler (which includes a scene of the Expulsion of Heliodorus from the Temple) |
Wood inlay |
Aside from their practical liturgical purpose as choir seats/stalls, one will also note the many ornate carvings that are included within the design. Here, for example, is one of the panels showing David being anointed by Samuel, carved by Andrea Fantoni between 1705-1708:
In fact, many of the scenes in this particular work are taken precisely from the Old Testament.
Fantoni also executed other figures as part of the design, including these cherubs holding up a cloth bearing an episcopal stemma, presumably of the bishop of Bergamo who commissioned this part of the work.
This particular choir was accomplished however in two phases, with the first carved work being done by by Giovanni Carlo Sanz between 1693-1698. It is to whom that most of the allegorical figures can be attributed as well as the cherubs.