Briefly, it goes like this.
If you want maximum productivity, you go all out to perform, irrespective of any other factors. That is, if the production capacity is 100, you will achieve the full production capacity, irrespective of additional costs, people utilisation, market available, etc.
If you want optimum productivity, however, you have to consider a number of other factors, i.e. do you really need to produce upto maximum capacity, or in view of market prospects, cost of labour and materials, marketing costs, etc. etc. it would be more viable to produce say 70 only, being the figure that will give you the best returns.
Hope this helps.\
Jeroo