This service starts the reconstruction (concatenation of a point cloud relative to the SLAM pose).
Source code is available in - https://github.com/Parrot-Developers/slamdunk_ros/blob/Version-1.0.1/slamdunk_nodelets/src/pcl_xyzrgb_concat_nodelet.cpp#L90
This service store the reconstruction to a file on the Parrot S.L.A.M.dunk.
The procedure to record a point cloud is described here: http://forum.developer.parrot.com/t/can-i-record-point-of-cloud/4897
These services are useful to restart the various services you can subscribe to.
In the past, after changing the camera resolutions with dynamic_reconfigure, one had to restart the capture manually.
That is why this services existed.
Now this is done automatically so there is probably little reasons to call them.
The services are declared here: https://github.com/Parrot-Developers/slamdunk_ros/blob/Version-1.0.1/slamdunk_node/src/main.cpp#L124
Sort of, for what we call reconstruction/xyzrgb_concat we are merging multiple point clouds.