There are too many pros and cons to go into full detail here, but I can get you started with the most controversial aspects of it.
1) Most people think of cloning as **Presto!**, here's a copy of a person. But cloning is at the cellular level. We can, in the future, clone tissue such as skin, bone or muscle, not to mention organs. This would be a huge medical advance, and instead of looking for organ donors and taking anti-rejection drugs for the rest of your life, we could actually clone your kidney or spleen.
2) This could save some animal species from extinction, and potentialy even resurrect some that have already gone extinct.
3) We may discover cures or treatments for myriad diseases and conditions, such as Alzheimer's disease or Multiple Sclerosis, by cloning a person's healthy tissue and allowing the body to regenerate.
1) We do not know what we're doing. Human life is not to be experimented with at such a basic level, as this could and would be abused by governments, companies and individuals. In other words, we cannot handle such technology.
2) In eventually creating another human being from scratch, what legal rights will clones have? The same as humans? What about the early versions of clones that will probably be imperfect as the technology is still new?
3) There are religious/spiritual objections to the idea of cloning, arguing that, in this case, it is dangerous and wrong to mess with God/Mother Nature and that no one has the right to create life in this way when there is a natural way.