There are several times you would need to have multiple versions of Corona installed on same computer.
Corona releases a new version when there is a major issue fixed or a when a bunch of fixes are made. Some time you would need these advanced features to make a new app and at the same time you need its old version to test an existing app.
But this is not possible in Windows. However , this is possible in Mac.
“On Mac, you can have many Corona SDK builds installed at the same time. The trick is to rename the CoronaSDK folder in the Applications folder after installing a new version.”
“For Windows, you can only have one version of Corona SDK installed at a time. You don’t have to uninstall when installing a newer version, but if you need to install an older build, you have to uninstall first.”
Also , FYI – Corona allows you to install and register it with one single user id for two instances of installations at a given time. This mean you can use the same Corona Id for two installations.