While EFT is often described as a self-help tool, and it can be used on one's own with remarkable results, often working on one's own is insufficient to address all the deep issues that may be uncovered with EFT. You may also experience some of the benefits of EFT, but hit a block that you may not have enough tools to overcome and you may give up on the issue and on EFT. Skilful application of EFT works almost every time and for almost every issue, but it takes training and experience to use it properly.
A certified EFT practitioner is trained to use investigative tools to uncover the root causes of problems, to find and address every aspect of an issue to make sure that those aspects do not bring negative emotions again in the future. With some issues an EFT practitioners can gently clear the issues that you might be scared or uncomfortable to address on your own. An EFT practitioner can also be your coach who can help keep you on track in doing your own tapping.