Okay, the truth is that you are going to see ads where ever you go on any Google property including inside your GMail account, so why not tell Google what you would like to see?
Well, you can. You can click this link while logged into your Google account and tell Google the types of ads and ad categories you would like to see.
What I find interesting is what Google has already identified for you. With that information on the page, you can add, edit or remove preferences. Why not make the advertising you are going to see anyway more tailored to what you might actually want to see? To me that makes perfect sense. Remember Google is collecting this information, but it is not personally identifiable to you to third party advertisers – just Google.