Working in a Unixy system, I am often confused by where to store downloaded packages. For example, I'm trying to install Spark on OSX, following these instructions. When I get to tar -xvzf spark-1.1.1.tar, I wonder if I'm really supposed to do this in /Users/me/Downloads, which is where the downloaded tar package has automatically stored itself. Is this really the best place to store the package, or is there a conventional place to put them?I periodically clear out my Downloads folder, so I worry that deleting the original files might cause problems. 
Is there a conventional place in Unix to store downloaded packages?
directory structure;download