1.It's easily accommodate when speed reduction/increase of up to seven to one.
2.Long shaft-center distance is accommodated,and makes the chain more versatile.
3.Using chain with multiple shafts or drives with both sides of the chain.
4.Standardizaation of chains makes selection easily.
5.Cutting and connecting chains is easily.
6.When transmitting the same torque,a chain system can use samller sprocket deameter then a belt pulley.
7.Sprockets distribute the loading over their many teeth,so the wear is less than gears.