I’m sure others are more experienced than me, so please take my findings as hearsay.
There are two ways to cut through material. The first way uses more power. The second way uses a slower speed – so the laser lingers over the area for a longer time.
So 500/41 may be the same as 1000/75 on that material. (Slower with less power is the same as faster with more power.)
So why use lower power? The laser is like a lightbulb. The longer it runs at full power, the shorter the lifespan. So if you can get away with less power then it will last a lot longer. (I don’t think the tradeoff is linear; if you can reduce the power by half then you increase the life by more than double.)
The other thing to remember is the quality of the line. This shows up with some material more than others. Basically, fast cutting results in rougher cuts. Show cutting results in smoother cuts. You’ll see this on really curvy edges. This is kind of like the LPI setting with engraving: at 225 LPI, you might see raster lines. 340-600LPI typically has no visible rastering. (And bigger LPI means more overlap in the laser strikes. So on thin material, like paper, you can often cut using engrave with a slower speed and high LPI.)
Edit: I stand corrected. Lower power doesn’t lower life.