What’s the difference between Uri.ToString() and Uri.AbsoluteUri?

Given for example:

UriBuilder builder = new UriBuilder("http://somehost/somepath");
builder.Query = "somekey=" + HttpUtility.UrlEncode("some+value");
Uri someUri = builder.Uri;

In this case,
Uri.ToString() will return a human-readable URL: http://somehost/somepath?somekey=some+value

Uri.AbsoluteUri on the other hand will return the encoded form as HttpUtility.UrlEncode returned it: http://somehost/somepath?somekey=some%2bvalue