Witnesses, Advantages
Although Pennsylvania Wills are not required to have any subscribing witnesses, there are certain advantages to using witnesses that must be considered.

When there are subscribing witnesses it is presumed that the testator was of "sound mind" at the time of execution and anyone who contests that will has the burden of proving otherwise. Without subscribing witnesses, the proponent of a contested will has the burden of proving the existence of sound mind.

Also, all Wills offered for probate must be proven, which requires two people to sign an affidavit for the Register of Wills stating that the signature on the will belongs to the testator. Having subscribing witnesses does not remove this requirement, but provides two people who may be looked to first to prove the will.

See: Self-Proving Affidavit; Wills Without Witnesses; will Contests, Generally