Speck Electronics LiLo - Manual (Page 33)

When depressed, this switch disconnects the chassis ground of the LiLo from
the power DC common. This can reduce the chance of ground loops and
eliminate unwanted hums or buzzes.
A few words about hums, buzzes, and the role of a ground lift.
Not to suggest that the reasons for hums in an audio system can't be
explained…they can… but the explanation, cure, and costs are very often out
of the reach of the average project studio. This is why manufacturers
sometimes include a ground lift switch on their products. It just saves you the
trouble of clipping or soldering ground wires on your cables. Hence, there is
not a right or wrong position for a ground lift switch. If either position
improves an otherwise hummy-buzzy situation, that is the right position.
Chapter 3 Operation Section 29
54. Chassis Ground Lift