Pros and cons with everything my friend, If you deicide to overclock your CPU you may reduce the life span of it, increase heat from the CPU and run the risk of killing your PC (unlikely but can happen). Pros is that it gives the computer a boost, you may notice this using demanding apps or playing games.
If you're new to this I would highly suggest reading the OC101 sticky and doing your homework about the CPU & other hardware e.g. RAM/mobo etc... and see how far you can push them.
Also another thing to think about if you do go for a good OC, you may need to buy better aftermarket cooling for your PC... Fans, heatsinks and so on.
There are loads of PC benchmarking software and stability software out there too which will help you get your PC "tuned up" nicely.
Overall I think OC'in is great, to get that bit extra out of your system for a small fee. So I say go for it.