One very specialized application I could think of is the slab/wall joint for a round prestressed concrete tank. This prevents problems during seismic events. It also reduces the moment that normally will occur at this joint in a tank.
If you are speaking of an isolation joint between a slab and a wall in a building, its function is to allow shrinkage of the slab, since the slab is generally poured many weeks after the wall is poured. We call it a "bond breaker". I think most contractors use a compressible bituminous filler conforming to ASTM D994.
