It avoids modeling very long sequences, as the character-based models do, by preserving trivial compositionality in consecutive alphabetical letters and digits.
the separation between letters, digits, and special tokens explicitly represented most of the idiomatic syntax of Bash we observed in the data: the sub-token based models effectively learn basic string manipulations (addition, deletion and replacement of substrings) and the semantics of Bash reserved tokens such as $, ", * , etc.