Reactivity/solution_05b uses rbind more than necessary

[grntlngdn]

Is there a reason that the following doesn't demonstrate a more efficient solution?

  rv <- reactiveValues(points = cars)
  
  # Same as Solution_05a.R, but instead of keeping
  # track of the single most recent point, we accumulate
  # all previous points using rbind().
  observeEvent(input$click, {
    if (!is.null(input$click)) {
      thisPoint <- data.frame(
        speed = input$click$x,
        dist = input$click$y
      )
      rv$points <- rbind(rv$points, thisPoint)
    }
  })
  
  output$plot <- renderPlot({
    df <- rv$points
    plot(df, pch = 19)
    
    model <- lm(dist ~ speed, df)
    abline(model)
  })
}

As Joe Cheng does, I'd like to recognize that while rbind works fairly quickly usually, it seems like this demonstrates how things could be done slightly more efficiently in general