Commerce Cart Expiration is a really useful utility for removing old carts that may be abandoned. It will help you to have your order list cleaned up and most important, to release resources and stock if needed. You can set up a time condition and number of order elements in the default rule provided by the module or alter it to provide your own defaults. This rule is cron based so it can be triggered at any time.
Additionally, this module also provides a nice drush integration that uses the rules configuration settings for expiring old carts and this way expire them from the command line or an automated process.