I think my knowledge of exporting images at different resolutions for web/screen and print is pretty old school...
I am under the impression that it is necessary to export 2 separate files of the same image if needing to display on the web (or simply a screen a such as a TV) and also for print. The web version being 72ppi and the print version being 300ppi...
Is this correct or what is the optimum/most efficient way to do this?
Ppi (Pixels per inch) is metadata used by printer drivers to calculate physical dimensions of a print.
For instance, an image with the pixel dimensions 2400 x 3000 and the ppi set to 300 will print at 8 x 10 inches, because 2400/300 = 8, and 3000/300 = 10.
Physical dimensions are not a property of digital images, but Lightroom lets you enter physical dimensions in the export dialog and does the math for you, and exports with the correct pixel dimensions.
For web images, the ppi number is irrelevant, i.e. it has no effect on an image viewed on screen.
The image will display according to its pixel dimensions, regardless what number you enter in the ppi field.