Imagine your home. If you overfill it with furniture, then to walk from one room to next, you would have to move a few pieces of furniture around.
So while your home’s overall space doesn’t change, the amount of furniture in it if overdone can turn a 5 second walk into 3 minutes of exercise – a situation best avoided.
Same with storage space on PCs – leave 10% free on large drives (32GB+), 20% on smaller ones (16GB and less). 16 to 32 – Grey area, try for 15% (for typical home usage)
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