The decision to let a vertical spread expire or close it before expiry depends on several factors. These factors include the current profit or loss on the trade, the remaining time until expiry, and your expectations for the base asset. For debit spreads, if you've already achieved a significant portion of the max possible profit, you might choose to close the trade early to lock in the gains. For credit spreads, if the contracts are still out-of-the-money as expiry approaches, and you believe they will remain so, you might let them expire worthless and keep the entire premium.