Are there a lot of inactive items in your Assigned To Me report?
Sometimes the workflow has been configured so the person who fixed or resolved an issue stays assigned to it after it's finished to keep record of who worked on it. It's not necessary to do that. You can rely on the record history, which is a full audit trail of everything that has been done on the record, to have that information. Or, you can create a User Pulldown to capture that information and use it to run reports.
To take advantage of this option, configure your workflow such that a record is assigned to "TBD" when it is closed or resolved or put in a state where it will no longer be processed. TBD is a built-in user that can signify no one needs to work on the record. Then, use the info in the User Pulldown Knowledge Base article for details on how to create this type of field.