Ideally the SSAS database has all the measures you need but now you have the capability to add new ones if you need to.
You can control the folder (table/measure group) under which the new measure shows up by using the “Home Table” option from the Modeling tab. I really like this feature as you can create copies of the same calculation and send them to different folders for ease of use.
If you’re interested in getting this added to Multidimensional as well, there is a request you can vote on.