This is a common question, as there are so many EFT videos on Youtube, apps to help you and pre-made scripts to tap to.
These ‘canned’ scripts and approaches are all absolutely wonderful & if they help you, by all means, use them! They have also helped make EFT more of a household name to many thousands of people.
So why work with a practitioner?
Firstly, because everyone is unique & therefore their experience is unique. With clinical EFT, the more specific you are, the better your results. This means that a ready-made script may not be specific enough to help release the issue that you are dealing with.
Secondly, there is a very real danger of flooding yourself with emotions and trauma if you get triggered into a traumatic past experience. A practitioner is able to hold the space and help regulate you during a session when dealing with a traumatic memory.
Thirdly, there are a number of techniques in EFT (Emotional Freedom Techniques), and you learn more about these when working with a practitioner.
I have personally liked the pre-made scripts, but only really found profound benefits when I worked with a practitioner.