What are "concretors' nippers" for?
These are used to tie rebar wire around rebars - twisting the wire around the rebars, and then cutting the left over. Rebars are used prior to pouring the concrete to strengthen the concrete, hence the tool name.

They are also called "end-nippers", and are useful for cutting or grabbing things close to the 
surface, such as nails or the like. Finally, they can be used to cut tiles, however I have no experience with this function and can't comment on it.

See this nice little PDF that shows a picture of the two uses of this tool (no affiliation, just what Google came up with).