What's the deal with umbrellas at the fancy dress store?

[HordePrime]

Umbrellas, available to buy at the fancy dress store. What is the point?
If I buy one, does my sim use it all the time, do I have to use a wardrobe to make my sim use it (and then again for them to discontinue using it), or is it like a swimsuit; they use it automatically if and when the need arises (such as using a weather machine to make it rain)?

Thanks.

[ErinPW]

Umbrellas, available to buy at the fancy dress store. What is the point?
If I buy one, does my sim use it all the time, do I have to use a wardrobe to make my sim use it (and then again for them to discontinue using it), or is it like a swimsuit; they use it automatically if and when the need arises (such as using a weather machine to make it rain)?

Thanks.

It's like the swimsuits, except the swirl around. They take it out of their magic pocket when it's raining.