What makes Time Machine necessary if using iCloud? Does make sense to use Time Machine with external drive if I already have all my files stored in iCloud? What laptop information is Time Machine keeping that cannot be stored in iCloud?
Time Machine can, in theory, restore the exact state of your Mac at any time. All apps, prefs, settings, documents.
iCloud will restore only your documents. Everything else would need to be re-installed from scratch.
Whether or not you consider that 'necessary' is your call.