Wiring Dual Electric Fans Question.

I am not sure if I want to wire my two fans so that they kick on together or have two sensors so that the fans kick on at different temps. The down side to two sensors is a little more cost and a little more wiring. What is the downside on having both fans kick on at the same temp?

Thanks,
Rod

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I wired one to the sensor and one on a toggle that could be turned on when needed