It follows the file changes as they occur and shows you the output. This is an alternative for tail -f filename. For example the following command will show the first 15 lines of the file file_name.txt. This command does the opposite task of tail. This is the best choice for reading growing documents. It's really useful if you are watching some logs, for example. Imagine to have a empty document, that is filled while you are watching it if you want to see new lines in real time while they are written to the file without reopening it, just open the file with the -f option. There's another use case where this command is extremely useful. To read last 3 lines, we need to write: tail -3 file_name.txt The above command will show last 10 lines(default) of the file. It's useful if you need to read just a few lines in the end of a very big document.
This software shows only the last part of the file. This is the best choice for reading medium to big documents.
Using Ubuntu you have different ways to read a text file, all similar but useful in different context.