Example: 5 x 18 = (5 x 10) + (5 x 8) instead of 5 x 10 + 5 x 8?
Early in their education (even well into learning algebra), students don't naturally see the structure within algebraic expressions. It takes a bit of mental overhead to see that 5 x 10 + 5 x 8 is the sum of two products.
Presenting the expression as (5 x 10) + (5 x 8) saves students the mental overhead, letting them focus on the message that's trying to be communicated.
I recently found myself adding unnecessary parentheses to first-order logical formulas in order to make them easier to read, and thus more effective at quickly communicating the idea I was trying to get across.