As opposed to hour tallies.

I have tried both approaches while working. But have found that working towards milestones focuses my energy much better than working towards hour tallies.

Plus, there is an element of excitement in achieving milestones. Which is not the case with hour tallies.

You can think of it this way.

When you are earning, more than the dollar/rupee number (hour tallies), it is the things you buy (milestones) that matter more.

Here's an excellent blog by Cal Newport, where he explores living (and working) deeply in a distracted world, among other things.