Fast loading applications A more responsive OS, faster loading game levels
basically with fragmentation, a file gets split into sections on the hard drive, so say a file is 4 parts, 1 could be stored at the end, 2 at the start, 3 at the end, and 4 at the start
so the drive has to move from each end back and forth to read the file (which will take a bit of extra time)
if the file had all parts 1234 right next to each other on the drive it'd read it in 'one go'
so de-fragmentation is important
give o&o defrag a trial, works wonders!