Over time errors build up either through chance or poor programming causing the use of additional resources, when you reboot everything gets set back to normal.
There is probably not a big difference between Mac and Windows, but windows have historically had a lot of really crap programs written for it and because it’s been much more open than Mac is much more acceptable to random issues. Such as a badly written drives for the cheap video card from who knows where no one should be using vs the video card apple wrote the driver for.
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