I think it can be useful even if you're able to save / invest "easily". I'm in that situation. I'm fairly thrifty and don't spend much. But after looking back

I think it can be useful even if you're able to save / invest "easily". I'm in that situation. I'm fairly thrifty and don't spend much. But after looking back over my spending, I've realized there was enough useless crap that I could cut out. For example, I realized I was spending an enormous (to me) amount on lunches at work, though it was nothing fancy. It's just that I was working in a rather touristy / "rich" part of town, so aside from a pastry, everything was above €10. I started packing my own lunch most of the time and the cost went waay down for no discernible loss. Bonus points for eating less and losing some weight, but that's a different story.