Slicing refers to the process in which a file for printing is processed through a special program (the slicer) that makes the file readable to a 3D printer. Slicers are available in both propriety and open source version. Many printers will accept a variety of sliced files or G-code from a slicer, although some manufacturers prefer their own software due to the advent of special features and the battle for efficiency and speed in printing.
Some differences in slicing softwares include but aren't limited to;
-Support type, some print tree-branch style supports, some print vertical ones
-Printing style, some raise the bed up and down while jumping from point to point for example
-Efficiency, some printers create G-code faster than others, and some allow printers to print more effectively in terms of filament usage
-UI; some have advanced options such as filament retraction, high speed printing, or are able to interface with a Webcam, other computers and printers etc
Having a solid file is important for most forms of printing. In SLS printing, errors normally result in weak but stable parts, or floating pieces. In FFF/FDM printing, errors in files result in air printing, disconnected parts, long render times or unresponsive printers. Having a solid file with correct faces and verticies, where all meshes are connected is extremely important in FFF/FDM printing. This can be adjusted by user correction in the CAD software of their choice, repair functions in the slicing programs or use of an online/cloud repair service such as Microsoft's Netfabb Model Repair Service.