Yes. The sensor-plane marker shows the exact position of the image sensor (or film plane) inside the camera body. Its main practical use is for precise distance measurement from the subject to the sensor plane, rather than to the front of the lens or camera body. This can help when:

• setting focus by distance using a lens distance scale
• measuring exact camera-to-subject distance for technical or macro work
• calculating reproduction ratio / maximum magnification in close-up photography

For most everyday photography, you usually don’t need it. It becomes more useful in controlled situations where focus distance or magnification must be measured accurately.

Other brands also commonly include a similar film/sensor-plane mark on their camera bodies, including DSLRs from makers like Nikon.