This topic is discussed in section 4.6 of the ISOCAM Observer's Manual. Several tests have shown that micro scanning (i.e. CAM01 in raster mode) should be used for faint, as well as extended sources, providing that the raster is large enough. Beam switching (CAM03) is recommended for only very faint sources. Otherwise, enough stabilisation time should be included at each beam switch position to take into account of detector memory effect. For most observations, the microscanning proves to be more efficient than beam switching in term of observing time, and achieves the same sensitivity. This is a change in recommendations from section 4.6 of the ISOCAM Observer's Manual.
Beam-switching is also recommended for bright, high-contrast sources; for example, to probe the neighbourhood of bright sources looking for faint extended structure or faint point sources. Under these circumstances, a raster will carry a lot of ghost images due to the memory effect of the detectors. This can be avoided by making a beam-switched observation instead; in this case, the observation should have only one off-on cycle and should start at the background position.