In some cases it could be handy, if you were able to convert a container you've constructed in the variable pane into a type directly from the variables pane.
One case could be, if you chose to store some settings in the sequence file, but the settings are dependent upon fx equipment or the product variant. It can be handy to have a variable with the settings, and an array of settings specific to various configurations from which you can choose. But the 'settings' container and the type in the array of settings containers, of course have to align. And this is best achieved by a custom data type.
Often sequences start out for one configuration only, and later on the need for multiple configurations occurs - and that's why I think it could be handy - if you were able to convert a container, already in the variable pane, into a custom data type.