WPF: ControlTemplate vs Style that Changes Template

Inside App.xaml I may have:

<Style TargetType="{x:Type Button}" x:Key="roundButton">
  <Setter Property="Template">
     <Setter.Value>
        <ControlTemplate Target="{x:Type Button}">
            bla bla bla...
        </ControlTemplate>
     </Setter.Value>
  </Setter>
</Style>

vs. just going

<ControlTemplate Target="{x:Type Button}" x:Key="roundButton">
    bla bla bla...
</ControlTemplate>

I'm confused, which should I use开发者_如何学JAVA / what's the difference?

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Using the Style you could also change other values of the button at the same time. Using the ControlTemplate you can only change the template. So which is appropriate?