Often you are trying to replicate the fileshare structure on the SharePoint site which means multiple folders migrating to multiple libraries. It is tedious to go and add 'Source' for each folder. It would be easier to provide a grid view side by side (common in FTP file transfer tool) where you can map folder to document libraries to migrate the data. I did a migration for 25 folders from fileshare and I had 25 different libraries and it was unnecessarily tedious. I know I can create a csv/json for this type of migration but it would be easier to have it in the UI.