Good option if you do not mind getting pregnant. Most people do not use the sponge correctly, so women often wind up pregnant. If you do not want to get pregnant or have a baby, think about using a different method.
You are comfortable with your body. If you are not okay with putting your fingers inside yourself, the sponge is not the best option for you. It is a lot like putting in a tampon, though: if you can do that, you can probably manage the sponge.
It takes discipline. You have to remember to insert the sponge every time you have sex. You will need a bit of self-discipline and planning. But at least you can carry it with you if you want.
Allergies? You should not use the sponge if you are allergic to sulfa drugs, polyurethane, or spermicide.
The pregnancy question. The sponge has no hormones, so you will be able to get pregnant as soon as you stop using the sponge. Protect yourself with another method if you stop using the sponge and do not want to get pregnant.