Need to Sweep

I play mainly Aerosmith, guns n roses and Metallica. Also bits of kiss, lynyrd, poison, and zz top. ANd ive never come across sweep picking!
I sat down and began to learn it, realising i already knew partically how to do it because there things i play with a single sweep across four strings (not up and down). also in bohemian raphsody theres sweeps (i think).
Anyway, whats the need for people to practice it and build up speed in it? Is i just for show? I tihnk that sweeping sounds a but mechanical and naff at higher speeds.

Well, It's not mainly to show off for sure... It's basically used to play arpeggios with more speed... Anyway, you can play anything with high bpm to show off.

The most important thing to keep in mind while practicing sweeping (as with other techniques) is not to be in a rush to play fast , speed comes by time.
You seem like a Metallica fan (like me ;) ) , so I'll tell you where you can find easy sweeps in their songs to begin practicing.

1- Lepper Messiah Solo ... The begining of the solo is just 3-string sweeing throughout ... You should master this one as a first step, cuz you'll find these min/maj 3-string sweep a lot in other songs.

2-Creeping Death Solo ... There's a minor 3-string sweep there , in the middle of the solo as I can remember.

3-Fade to Black intro solo ... Some people play this one with alternate picking ... Anyway I prefere sweeping'em ... You should try sweeping too , at least for practicing... (what doesn't kill you makes you stronger).

4-The Call of Ktulu Solo ... There's a realy cool 4-string sweep in the middle of that solo , it's hard but worth practicing.

You should try some Malmsteen too ... You'll find the 3-string dim sweep in all of his songs !
Marty Friedman makes realy cool & complicated sweeps , Megadeth's "Rust In eace" should be your next step.
And for sure we can't forget the King of sweeps , Jason Becker.

I find the Ctulu part hard to sweep ´cause the tempo is to slow and it´s hard to get it tigh and even so I prefer alternate pickin´ at that part. Same wíth Fade To Black.

I totally agree with you man, Malmsteen-Friedman and the king him self Jason Becker. The ultimate sweep for me is the Serrana sweeps. But I must have a 24 fret guitar to be abel to play it.

Yeah man, Becker is a total insane sweeper... Sweeping from the 19th position till the 24th fret is definitly crazy ... You don't need only a 24 frets guitar , but you must make sure the 24th fret is pretty accessible too... I've played a lot of 24 frets guitar where the 24th fret isn't easily accessible... I find Jacksons & ESPs better than Ibanez at this point.

Also Friedman's sweeps is realy complicated . Due to his exclusive use of exotic scales in most of his solos, you find lots of legato stuff or even string skipping at the middle of a sweep.

And for Ktulu's sweep , I've seen Hammett alternate picks it on S&M video , and he does it on 3 strings only and a slide ... But personaly, I prefere the sound of a sweep, cuz all the notes sound very even and tight with sweeping.

I don't know what's your definition of (even & tight) , but I know that english isn't your or my mother language ... So probably we're both wrong in expression .. LOL :p

It's a matter of personal taste anyway , but for sweeping you play all the notes with only downstrokes or upstrokes at a time,so they have very similar sound and seems tight to me... That's how I like it.

Dude,

Fine either some Malmsteen songs such as Blitzkrieg, Far Beyond The Sun, Black Star, or something else.

Learn the arpeggiated section of Jason Beckers Serrena, I have a tab, one isn';t that hard to find, or something else by Bekcer off of his first album Perpetual Burn. Altitudes is full of shredding and good melodic sweeping and such.

Also the Metallica songs suggest above all have simple sweeping stuff in them learn those by all means.

Marty Friedman is always good on his own, i would suggest anything off his first solo album, Dragons Kiss...try Saturation Point, Anvils, or esepcailly Forbidden City.

Or you could learn some Petrucci stuff he does a lot of sweeping. Don;t know any Dream Theater songs myself but just look for one. I bet the song Hell's Kitchen has some stuff.

Also to answer you other questions, sweeping is used to play arpeggios faster, and arpeggios are just the notes of chords , so in the end it's more of a melodic device, though can be used in other ways to acutally play a solo more legato style with economic picking patterns.

Hope that gives you some more ideas..

Search the trick section for these names:

Anthony Layne and Leandro Spataro,

they've posted tons of sweeps. Actually I've posted some cool ones to so check em out.