I wanted to draw from a point to x and y axes using only one coordinate definition. From the very appreciated answers to this question and this question, I used the following code to achieve my goal. My original drawing has too many nodes and I was concerned about using too many names for the nodes. Then I tried the following code:
\documentclass{beamer}
\beamertemplatenavigationsymbolsempty
\usepackage{tikz}
\usepackage{pgfplots}
\begin{document}
\begin{frame}[fragile,t]
\frametitle{}
\begin{tikzpicture}[scale=.9, transform shape]
\draw [thick,-latex](0,0) -- (7,0);
\draw [thick,-latex](0,0) -- (0,7.);
\draw [thick, black, dashdotted] (1,1) node (o){} (o.center-|0,0) -| (o.center|-0,0);
\draw [very thick, green] (5,5) node (o){} +(-30:1.cm) -- +(150:1.cm);
\draw [thick, blue, dashed] (o.center) (o.center-|0,0) -| (o.center|-0,0);
\draw [thick, red, dotted] (2,2) node (o){} (o.center-|0,0) -| (o.center|-0,0);
\draw [thick, violet, double] (3,3) node (o){} (o.center-|0,0) -| (o.center|-0,0);
\draw [thick, brown, solid] (4,4) node (o){} (o.center-|0,0) -| (o.center|-0,0);
\draw [thick, brown, dotted] (6,6) node{} coordinate (o) edge (o -| 0,0) edge(o |- 0,0);
\end{tikzpicture}
\end{frame}
\end{document}
I got the following result:
I understood that each node should have a unique name. My question is how come all the nodes/coordinate have the same name, and still each drawing originates from its inline node; and even when using a node with the same name defined in another \draw command?

(...,...) node (o), you updates the coordinate associated too.center. On first lineo.center=(1,1), on secondo.center=(5,5), and it's not anymore(1,1). – Ignasi Aug 13 '18 at 11:43