The main reason behind using k-map is to reduce the boolean expressions having maximum 5 to 6 variables.
For solving equations having more variables k-map technique is very cumbersome.
K-Map is used widely because it is easy to solve and definitely gives the reduced boolean expression. if we solve a equation with boolean properties then the sequence of properties which we applied also matters so it does not give fully reduced equation if the sequence is wrong.
While reducing using boolean properties we are not sure that the expression is fully reduced or not . So we are never sure when to stop.