If you’re the one determining when the last day is, keep the following points in mind:

• First, check the employee’s contract for any obligations.
• If possible, some sort of notice is a good idea to allow the employee to wrap things up and to look for another job (i.e. in the case of a layoff due to a work slowdown). However, you will have to balance the notice period with the potential for sabotage from the employee. Generally if someone is being fired, it’s best to remove their access to property and equipment at the time of the termination meeting.
• If the firing is due to a serious incident (theft, fraud, criminal activity, refusing treatment for substance abuse, ongoing personal issues with others in the office that this employee incites), it’s probably best to end their employment then and there. Severance may reduce the likelihood the employee will file a complaint, but is entirely up to you and the usual practices of the company.
• If the employee has access to proprietary or confidential information, or has access to the company’s internal e-mail, internal computer drives, etc, it’s also probably best to end their employment then and there. This practice protects you from sabotage and them from suspicion if anything does go wrong.