What does Twitpic do on your Twitter account?

[one of twenty]

I'm thinking about using Twitpic.
When I tried to log on using my Twitter account this is what it says:

This application will be able to:
Read Tweets from your timeline.
See who you follow, and follow new people.
Update your profile.
Post Tweets for you.

What exactly does this mean? What are some updates it will do to my profile? What does it mean it will post tweets for me?
I'm new to this. Any help is much appreciated.

[one of twenty]

Allows you to easily post pictures on Twitter