Ancient Greeks used the butterfly as a symbol of a human psyche. Wings can symbolize resurrection after death or your rebirth. But not exactly in Ireland: there they symbolize dead souls waiting to enter the purgatory.
They are also a symbol of miracle of life in all the (ancient and modern) cultures. Imagine, going from a worm to such a beauty. This fact makes such a tattoo also a good way to express your own personal life transformation.
Most men wouldn't get a butterfly tattoo, but many are fascinated by the versatility of this design. You can use one alone, or even as an add-on as they are very easy to shape. In fact, a celtic butterfly tattoo can be formed by knots which form an image of a butterfly. In the tattoo artists' world, celtic butterfly tattoos most often symbolize the positive aspects of life such as grace and peace. BF tattoos can look pretty and peaceful and indicate freedom and all pervading happiness.
They are most often placed on the ankle, rail bones or lower back, or shoulder. Don't let the size intimidate you. A small girly butterfly tattoo can be very powerful if it fits your body and personality very well. A small one can have a surprising factor, especially if it's somewhere random and not symmetrical with another one. It doesn't have to be radical in size to have such an impact and expression. Even a not visible ankle one can make you feel more energetic. On the other hand, large tattoos have more room for detail.