Modern graphics cards generally have good coolers, but when they are full of dust, they do not perform as efficiently as they should. The turbo functionality of course works best when the cooling is in good order, and the GPU can get rid of its heat well. If your graphics card has become more and more clogged up with dust and debris over the years, the maximum clock speeds are achieved less often and are held for shorter periods of time.
Our GTX 960 had collected a nice - but not unrealistic - amount of dust and as a result we have seen in the test results. At 1127 MHz, the clock speed was more than 11 percent lower than when the card was clean. The clean video card, with and without a new cooling paste, also managed to maintain this higher clock speed with lower noise production. This is possible because the temperature of the chip was much lower; before cleaning we measured 84 degrees, while the cleaning resulted in a temperature reduction of 6 degrees. The new cooling paste achieved a further 2 degrees.
In short, after a good cleaning, your graphics card can actually run faster, quieter and cooler. This is an appealing prospect in itself, but with the summer heat also not an excess.