Should resources be freed at the end of onUpdate for watchface?

Should resources be freed at the end of onUpdate for watchface?

For example:

var globalFont;

function onLayout() {

  globalFont = WatchUi.loadResource("blah");

}

func onUpdate() {

  // render watchface

  globalFont = null;

}

I have seen people do this but it seems inefficient because you'd have to reload resources again on onUpdate every time.