You can delete a filter when it is no longer needed. However, since you can share your filters out with other users and they can create subscriptions, you need to keep in mind that the filter might be used by an agile board or in other places, as well as the fact that you may impact other users if the filter is shared. Luckily, when you delete a filter, Jira will inform you if other people are using the filter:

1. Browse to the Manage Filters page.
2. Click on the Delete link for the filter you wish to remove. This will bring up the Delete Filter confirmation dialog box.
3. Make sure that the removal of the filter will not impact other users.
4. Click on the Delete button to remove the filter.

Jira will inform you if the filter is being used by Jira or there are users subscribed to it. You can click through to see the list of subscribers, and then decide to either proceed with deleting the filter and letting the other users know or leave the filter in Jira.