Under what conditions do laboratories have the need to perform both, colony counting and cell counting?
Any lab that would like to make the distinction between live and dead cells in a cheap way would use both techniques. You count colonies on petri dishes to get the number of living cells, and count in counting chambers under the microscope to get the total number of cells.

There are easier ways to do this though, for example using this: https://www.thermofisher.com/de/de/home/brands/molecular-probes/key-molecular-probes-products/live-dead-viability-brand-page.html in a flow cytometer. That's not that cheap though.