What's the lowest part at the center of rear suspension?

Hi,
I changed the tires of my 90' Camry with a hydro-jack. The part
supported with the hydro-jack is the center of the suspension bar. I
find it is the lowest part and appropriate with the jack-jaw. A
question comes to me. What's usefulness of this part (like a half ball)
under the center of the suspension bar? From the user manual I can see
a hole at the lowest. Is it safe to use it to lift my car?

Thank you very much.

That's exactly what it is for - to lift the car using a hydraulic floor
jack.
The factory service manual shows this as an approved lifting point.
Apart from a centering structure to receive the lifting force, that
semi spherical protrusion has no function.