OpenLayers has a huge advantage as a Web GIS GUI over Leaflet. It can handle any projection, which can be described by Proj.4. Leaflet supports only two projections (the WGS84 and the Web Mercator). These projections are natively supported in most of the GUIs. As Leaflet is a plugin based, modular library, it has a plugin to use Proj.4 capable projections, but it makes a reverse transformation. It transforms the input coordinates with Proj4js from the defined projection to geographic coordinates. OpenLayers on the other side is capable to handle any coordinate system, so the input maps will be rendered in a projection defined by the developer.
Web mapping tutorial by Gabor Farkas is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License