Barebone kits are basically preassembled or half-assembled computer parts sometimes assembled and sometimes just loose parts.

-pros- 

Cheap- barebone kits are very cheap as opposed to you purchasing the parts individually, if you find the right retailers you will get them for a amazing price.The price is what attracts many to barebone kits.

warranty- Most Barebone kits will come with useful warranty, just if something goes wrong most big name retailers will let you return it for repair or refund. That’s assuming you did nothing to damage the parts yourself.

pre assembled- Some barebone kits come Pre-Assembled that’s beneficial to you since you wont have to do any of the work, if your not so computer savvy.

Options- Some people might think that they get more options when they purchase their computer from Name brand manufacturers but this is not actully true, you actully get more options Barebones. With Barebones you have the options of selections starting with the operating system all the way to what kind of video card it will have.

-Cons-

Reliability- you can’t always trust the parts that come with Barebones if they are not from a Reliable retailer the kit could have old used up parts. Sometimes the person that put together the barebone kit might have made a mistake but if you purchased from a well known retailer you will have no problem if anything goes wrong.

Shipping and handling cost- With barebone kits shipping and handling costs are higher because of the case but then again you will save here because if you buy the parts individually shipping costs will be up to your neck.