When the number of files needs to be listed is enormous, the process is batched. It can happen in both the methods of listing.
As mentioned in the apps script guide, maximum execution time of any add-on script is 6 minutes for Gmail & Google Workplace (G Suite) users. If you have to process a lot of files with so many nested sub folders, there are chances that Drive Explorer will exceed the max execution time.
In that case, Drive Explorer batches the process so that it can process as many files as it can. Batching is a workaround for the limitation Google has enforced. Under the hood, Drive Explorer takes a break for some seconds before getting back to listing your files. When batching happens, you will get to see a notification like the one below.
You can check the status of batch execution anytime by selecting, Extensions → Drive Explorer → Batch Execution Status.
Google Drive method can list hundreds of thousands of files without any issues. But, when it touches a million files, the browser runs out of memory and crashes. To avoid this, Drive Explorer pauses the process and shows an alert like the one in the image below.
You can resume the process by clicking on the "Click here" link. It happens when the number of files touches the 600 thousand mark. After the process is stopped, you can export the listed files & resume the process again.
When the process is paused, the folder size field will always be 'N/A'. To get the accurate folder size data, after all the batch processes are completed, click on the hamburger menu in the top left corner of the table and select "Export folder size data".