The second option adds the edge type “Follows” to the Edges worksheet in your dataset. It will get the followers from all users that are detected in your search query. The API will usually return the most recent followers first.
This option can easily max out the capacities of NodeXL and Excel. And it will take a long time to download the data. You can of course limit the number of followers to be collected, but still you might end up with more than a million edges e.g. if there are 1000 users in your network with an average of 1000 followers. That is way too much to handle for NodeXL.
There may be special use cases for this option, e.g. download data, export as .gexf and then analyze in Gephi. But we generally recommend to not use this option.