A noob needs a lecture on drop tunings

Typically 'drop' tuning means that the bass is tuned standard apart from the E string being dropped to the specified pitch - so drop D is DADG.

The 'why' varies. It maybe that peple like the feel of a 4-string but want access to a low D. Or that some riffs are easier to pull off with an open D than playing the 3rd fret on the B of a 5er - may guitar riffs are written in drop D, so for the bass to play in unison it would be easiest in drop D.

That being said, I've not had a need to alter my tuning yet - a trusty 5-string gets me through everything I need.

 

Instead of tuning a 4-string EADG, you "drop" the lowest string from E to a D.

It's mostly a guitarist thing IMO since it takes the shape of a power chord and makes it a simple bar for the guitars. Take F# for example. In standard tuning a guitar player would play the F# (2nd fret on E) with his index, C# (4th fret on A) with the ring finger, and F# (4th fret on D) with the pinkie. In drop D he could bar the lowest 3 strings with one finger at the 4th fret and achieve the same chord.

It does open up some cool new things you can do on bass though.

 

Lower tones; that's it. Well, maybe string feel as well.
I remember someone telling me that a half step down on all strings (E-flat, A-flat, etc.) is common in old Blues because of the extra bend you can get in the string and the darker tone you get. I really don't know if its true.
Your common Pop, Rock and Country will all be in standard tuning because most radio friendly music is happy bubble gum that wouldn't want lower tunings. Heavier music uses lower tunings because its, well, heavier sounding.
I haven't played anything in EADG except covers in years.
If you don't play music that encourages face smashing, there isn't a lot of reason to down tune. I happen to like face smashing.

 

Now that the original question's been answered, you have a few choices on how to enact it. 1) buy a five-string bass and you can play a D on the lowest string (usually tuned to B) 2) you can buy a Hip-shot extender which is a substitute tuner(machine-head) which you install on your E string tuner and has a switch which brings your E-string down to a D and back up again at the flick of the switch or 3) Drop-tune your bass's E string to D as required. I used 3) until I bought a five-string bass.

 

I also think some guitarists like the drop D tuning (just drop the first string a full step) because it lets them cheat on their power chords. A fifth chord with one finger is a lot faster than with two, so it allows them to play faster.

 

I double on guitar and bass so I'll throw my 2 cents in. Drop D was really popular with country players long before downtuned chugga metal. Yes it allows for 1 finger power chords but it allows for other things too. Having a pedal D to play over for example.

And like most generalities this is wrong quite often. Jason Aldean (not a fan but he's definitely popular) has quite a bit of stuff thats in Drop C#. Buck Owens did a lot of downtuning as did Waylon Jennings. Waylon and Clarence White both had banjo tuners on their guitars with stops that acted like a hipshot d-tuner. Like most things in music Drop-D is just an available tool that too many people pigeonhole out of ignorance.

 

It makes sense - the Country guys were really the ones using the Baritone guitar initially. In absence of an extra instrument and because the bass couldn't nail the right tone, down tuning and drop tuning was an easy way to get the extended range.