Definition of balance
By "balance" here we mean "balance". A player who is going to "balance his range" is a player who will have the worry of being impossible to read. For example, on the river, a balanced player will want to have bluffs and very strong hands when betting or raising all in. If a player is not popped and is bluffing too much on the river or not bluffing enough, he will be easy to read and the more experienced players will have no difficulty playing against him. If, on the contrary, he is thrown, he will be impossible to read.
Is it really necessary to swing his range?
If you play games at very high limits or if you always play against the same excellent players, yes, it will be important to balance your range so that it is not readable. On the other hand, if you are playing against amateur players who have a lot of weaknesses, you don't need to swing your range; rather, you need to exploit your opponents' weaknesses. For example, you are on the river in position and it is your turn to play. If you're up against a very conservative player who lays down too easily, bluff him often! If you have a good hand, bet small! Conversely, against a player who calls too much, don't bluff and only bet bigger on your good hands.