two forms of infinite decimal which are rewritten from finite decimal

Question

How to transform a finite decimal into a infinite decimal? It sounds nothing to discuss. But I have seen two forms to deal with it which make me confused.
Let's consider a finite decimal $x_0.x_1x_2\cdots x_n$. A possible form to rewrite it is $x_0.x_1x_2\cdots x_n00000\cdots$, referred to The Real Analasis Lifesaver writen by Raffi Grinberg. Another form is $x_0.x_1x_2\cdots x_{n-1}(x_n-1)99999\cdots$, referred to mathematical analysis textbook compiled by ECNU (East China Normal University).
I understand that $0.999\cdots =1$, because of denseness of real number, revealing two forms have their rationality. So the question is, is there any difference between these two forms, or is there any advantage of a particular form comparing to another?