The button on the User Options part of the tool bar of the main map page switches on the site's advanced functionality. This will let you use the full power and flexibility of the online maps site. You will be able to perform a variety of queries, access more information and have more control over which layers you want to see.
The online mapping site is a Geographical Information System (GIS) and, as such, will let you analyze and query all of the data it holds. The site is very flexible in the sort of analysis you can do. However, since you can ask questions that we haven't even thought of, we can't ensure that you always get a result to your queries.