They don't dry out the vagina like tampons
do. Because they are non-absorbent they catch only the blood and fluid
that comes from the opening of the cervix. The natural lubricating fluids of the
vaginal walls are not affected. This can help reduce the chance of yeast and
bacterial infections that are commonly linked with tampon use. However, it is
important that the cup is cleaned properly and rinsed thoroughly to prevent
introducing harsh chemicals into the sensitive environment of the vagina.
They do not cause TSS. Again, because they are not
absorbent they don't provide the environment that TSS causing bacteria like to
grow in. As long as your hands are clean when inserting and removing the cup, it
is changed regularly, and cleaned properly, there should be minimal or no risk
of infection of any kind.
It's internal, so you can go swimming, have a bath, or wear tight pants, and no one will know it's there.
It can be worn for up to 12 hours at a time. Cups can be worn in anticipation of your period starting, even to bed!. They just need to be removed and washed carefully at least once every 12 hours. So with a cup it doesn't matter if your periods (or your life) are clockwork regular or totally unpredictable.
They are very high capacity. All cups hold at least as much fluid as a Super Tampon, some will hold up to 3 times as much (because they don't also absorb extra fluid from the vaginal walls, they may last even longer). They don't have to be changed every 4-6 hours like a tampon does, so depending on your flow, you may only have to change it morning and night, or maybe three times a day.