Putting a piercing in an adult body of any size opens it up to the chance of infection. And even though your piercing heals, it will always be susceptible to infections because it is an unnatural hole in the body. The most common infections that are cited as being contracted from insufficiently disinfected piercing instruments are those of hepatitis (which causes liver damage) and HIV (which causes AIDS), as well as tetanus, bacteria, and yeast. And, as a side note, do not let anyone do any of your body piercings with a piercing "gun" of any kind, as these instruments cannot be disinfected.
Other risks: oral complications resulting from tongue piercings, such as chipped and broken teeth, choking on loose jewelry, speech impediments, and swollen, infected tongues; nerve damage (leading to permanent numbness in the area pierced); keloids (thick scars at the point of piercing); allergic reactions to the jewelry used to keep the wound open; the formation of deep cysts (which is a sac filled with fluid or semi-fluid matter); and other possible ill effects.
The other effect of body piercing is healing time, and here it is, by each area pierced: