by
Francois Bresse , Chief Engineer Electrical , Hage Industries S. A (Groupe Hage)
In my opinion it is not a question of power. it is more about re-inventing the wheel. The heart of a PLC is a micro controller. the benefit of a PLC is having an of the shelf solution to design and implement a logic program in industries. It all depends on what you want to do with it. designed a system from a micro controller demands much more programming and at a lower level, you would also need a good electronic knowledge, for instance to kill the noise at each output port to drive the relays. If you want to control an industrial machine it is a bit tedious. The PLC is much better since all of that is already built in up to the relays or transistors. If you need to install a control on a very small package then you re choice would be a micro controller. In all cases there is much more to it and the only true answer to your question would be "it depends".
Cheers,
Francois