It is not a requirement, but usually, Personal Representatives are compensated. Certainly, all personal expenses they incur in the management and process of settling the estate must be paid for. Typically, a personal representative earns a fee of +/- 2% of the total value of the estate for their work. This can be mandated by the courts or by law in some states and varies moderately from state to state. Generally, this percentage diminishes as a percentage as the size of the estate increases.
All funds paid to the personal representative are subject to approval by the probate court. Additional fees may be allowed by the court in cases of unusual difficulty or extraordinary circumstances. On the other hand, if a personal representative does not perform their duties in an orderly or timely manner, the court may reduce or deny compensation and the Personal Representative may be held responsible for any damages caused.
If a person is both the sole beneficiary of the estate, and the estate is not subject to Federal Estate Tax, it usually does not make sense to take any fees as all fee income is subject to income tax. (The money a beneficiary receives from the estate is income tax-free.)