Transfer tape really is a crucial element in making and applying vinyl designs. Sure if you are making small one piece items or large simple items you may be able to get away without it. But 99% of the time you really do need it.
When the vinyl is still attached to the original backing all of the elements of your design are exactly where they are supposed to be. The point of the transfer tape is to lift everything off of the backing and expose the adhesive. It will accomplish this all at the same time while retaining everything in perfect alignment.
Now the vinyl has a more aggressive adhesive than the transfer tape does. So when you stick your vinyl down to something the vinyl will stay behind, again still in perfect alignment, and the transfer tape comes off leaving your finished project.
Now this works best when you do what is commonly referred to as a “kiss cut”. This means that you only cut through the vinyl and not the backing too. Then you remove or “weed” out the unwanted vinyl leaving behind a square of backing material with your cut vinyl design sitting on it.
This video below from our friends at ExpressionsVinyl.com helps to clarify how this all works. If you are confused about the cutting you can check out our post on cutting vinyl.