A Big T trauma usually refers to an event where you were fearing for your life. This would include most accidents, all surgeries, and obviously any situation where you were super scared! Little t traumas would be all the other events that impacted you negatively, but you were not necessarily fearing for your life.
We treat these differently with EFT. The reason is to keep you safe. One of the goals of the practitioner is to hold a safe space for the client. This means that I will not let you get re-traumatised! Imagine someone with a phobia for spiders & when they walk into the practitioners office, they get a spider thrown at them! I would leave in a hurry!
Sometimes exposure to the trauma can help heal, but there are gentler tools to achieve exactly the same thing. If you practice EFT by yourself, it is best to work through Big T memories with a practitioner so that they can keep you safe.
One of the ways that the gentler techniques work, is by creating distance from the actual event, while still engaging with it. Obviously the tapping also brings a calm to the body, which is essential for healing.
On a last note, just because something is classified as a little t trauma does not mean that it has less of an impact in your life! We can quite easily build patterns of belief or habits from little t events.