In MongoDB you have two options to remove all the documents in a collection.
thought the output of above two statements ( removing the all the documents in a collection) is same, there are couple of differences with two options.
remove will remove document one by one where as drop will remove all the documents at once. So in case you are dropping documents of a large collation, drop will be much faster than the remove.
However, drop will remove the meta data related to the collection as well. for example, it will remove the indexes associated with the collection.
So if you want to remove all the documents in a large collection, better option is use drop statement and recreate indexes again.