Their advantage lies in their compactness; larger telescopes can be accommodated in smaller domes. The complete payload can be used for instrument weight, no counterweight axis is needed. ALT AZ mounts, however, have to track in three axes (ALT, AZ and derotator at camera/eyepiece) which is technically more demanding but no longer a problem due to modern computer technology. The smaller ALT-AZ mounts are often used by amateurs and public observatories for visual observation. The larger ones are used for satellite tracking, where the alignment of the mount to the earth axis is not necessary or even disadvantageous.
