As a catalyst, ArMs have three advantages,
# thanks to the development in molecular biology, it is quite easy to generate a library of ArM mutants which has a size up to 10. Using proper selection method, the ArM has a large potential to gain unique catalytic properties. 
# ArMs are proteins, it can have both hydrophilic and hydrophobic surface in the aqueous solution. Anchoring the artificial cofactor which is not easily dissolve in water would help it function in aqueous phase. In some structure, the hydrophobic cavity would protect some labile bond (like many carbene or nitrene-metal complex in Arnold ArMs). 
# The backbone itself in ArM is a asymmetric environment. In some cases, the enantioselective synthesis can be tuned by changing one or two amino acid residues around the metal catalytic center.
So far, ArMs can catalyze a lot of chemical reactions, such as: allylic alkylation, allylic amination, aldol reaction, alcohol oxidation, C-H activation, click reaction, catechol oxidation,  reduction, cyclopropanation, Diels-Alder reaction, epoxidation, epoxide ring opening, Friedel-Crafts alkylation, hydrogenation, hydroformylation, Heck reaction, metathesis, Michael addition, nitrite reduction, NO reduction, Suzuki reaction, Si-H insertion, polymerization (atom transfer radical polymerization).