Random letters containing comments

Occasionally I get a feedback form or via the blog comments, messages that appear to be random, however, that the e-mail addresses and web addresses are in the correct format, for example ksdjhfieruhghbviu.com. What are these and what benefits to the sender?

 

I do that all the time when I don't want to give out my info. Looks like filler.

 

This seems to be filling, but what use is that the sender if all the fields (name,email,www and message) are full of it? With no effective link to the actual existing address.