If the last Naira spent on each commodity by a consumer gave him equal satisfaction, it means the consumer has been able to

This question describes a condition from consumer equilibrium theory. When the last naira spent on each commodity yields equal marginal utility, the consumer has achieved the optimal allocation of a limited budget. This state is known as utility maximisation.

The principle is formally stated as the equi-marginal principle (or the law of equi-marginal utility):

\[\frac{MU_A}{P_A} = \frac{MU_B}{P_B} = \frac{MU_C}{P_C} = \cdots\]

where \(MU\) is the marginal utility derived from a good and \(P\) is its price. When this condition holds, the consumer cannot increase total satisfaction by reallocating spending from one good to another, meaning total utility is at its maximum given the budget constraint.

Maximising costs or cutting costs are objectives that apply to producers, not to consumer choice theory. Increasing profits is similarly a producer's goal. The concept described in the question is purely about a consumer arranging purchases to get the greatest possible satisfaction from a fixed income.