Every now and again someone asks me about “that little checkbox at the bottom of QGIS.” Look at the picture below to see what they’re talking about.
The Render box is checked by default in QGIS. When it is checked, all active layers in you map will be rendered, or created, every time you pan or zoom on your map in a scale-correct manner. It will also re-render your map every time you turn a layer on or off.
What happens if you accidentally un-check the Render box? You can still zoom and pan, but the map will be treated as a static image and will look very pixelated. The symbols for point data won’t change size relative to other features as you zoom (see left). If you turn layers on and off, they won’t change.
Every now and then I’ll intentionally turn off rendering, mostly when I’m adding lots of large layers at once and I don’t want them to all show up one at a time as they load. You can learn more about QGIS rendering in the General Tools documentation (here).