basically what the names inply...serverside code is run on the server while clientside code is run on each individual users pc.If you run everything as serverside code you have 100% control on what it can do because it is running on your server...but with clientside, users all have different browsers with different settings, you have to try and accommodate all the diffrent browsers and try and foresee problems with possible settings the user has on their pc (which in some cases is impossible).