The transformation parameter is 'optional' because it is unnecessary when the input and output geographic coordinate reference systems are the same. When they are different, the parameter becomes mandatory in the Project Tool.
If the output coordinate system is WGS 84 (latitude-longitude), you don't need to project it. If the needs to have a different version of WGS 1984 (name is different), use the Define Projection tool instead. That will update the 'metadata' and not change the coordinate values.
Another method is add the data to ArcMap. Set the data frame's coordinate system to what you want to use. Right-click the layer in the table of contents and select data, export data. In the dialog, choose to use the data frame's coordinate system.
Melita