The difference of drop D from standard tuning allows for the three bass strings to form a D5 power chord, which can be shifted up or down the fretboard with a single finger (usually the index) to produce any power chord quickly and easily. Drop-D also enables the guitarist to play a step lower than in standard tuning, and many artists value this deeper, fuller sound.
Dropped D tuning is perhaps most widely used in heavy metal or rock music as they take full advantage of the easier power chord transitions needed for extremely fast playing. However, the tuning has also been used in many other types of music, including blues, country, and folk. Most modern metal guitarists use or have used Drop D tuning.
This tuning may be the most prominent tuning in modern rock and metal, but it is not uncommon for these guitarists to play in E-flat tuning/down tuning or dropped C tuning.
Drop D also allows fingerpickers to play chord shapes higher up the neck while maintaining an alternating bass.
Drop D is for people who are actually capable of playing the guitar FAST.