Unhiding / Hiding rows based on a different cell value

You may also try:

Private Sub Worksheet_Change(ByVal Target As Range)

If Range("H11") <> "" Then
Rows("13:15").Hidden = True
Else: Rows("13:15").Hidden = False
End If
End Sub

or:

Private Sub Worksheet_Change(ByVal Target As Range)

If Range("H11") = "False" Then
Rows("13:15").Hidden = True
ElseIf Range("H11") = "True" Then
Rows("13:15").Hidden = False
End If
End Sub

Also see the "Please consider" note at the bottom of this post.