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What is the impact of archived work items?

Version: RTC 5.0.1 web
If I archive work items, are they automatically excluded from Plans? How does RTC handle archived work items in general?
Context: Our Product Backlog plan is getting very big because I suspect the system loads all resolved items as well (even though I've excluded them from the plan, but it still mentions the amount and including them goes really quickly). I was wondering if archiving some resolved work items from previous iterations would make the Product Backlog quicker (as well as reports, queries, ...).