I know a couple people who've run without them. I wouldn't worry too much about it, just plan on taking them off periodically to clean any accumulating dirt out to prevent it from building up. Put a plastic bag over them if you ever end up hosing out the engine bay.
I gotta say though... I think they look pretty ugly sitting there by themselves.
I suppose that other than just keeping dirt and water out they may also serve to prevent the actuator from heat soaking.
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