I do 60, 20, 10, and 5 minute hop additions plus a steep. Why? Because I like the results. Objectionable aromas like cat pee and onions seems to be reduced or eliminated with some boil time. I don't steep hops that are prone to foul aromas.
I'm finding the opposite. Some hops like Citra seem to stay soft and pleasant when they are not used in the boil. I have to wonder if there is some sort of isomerization reaction that creates those off aromas like cat pee and garlic? It does seem limited to certain hop varieties.
The results of this study are consistent with my observations.
4mmp = potential for cat pee
I read that study a bit differently. 4MMP is decreasing in the boil, but increasing in fermentation. This says to me that the 4MMP is being chemically bound during the boil (and the authors also refer to two studies that have indeed found that is is happening), and then released by the yeast during fermentation. Since 4MMP has a flash point of 129F, it looks like this conjugation may have a protective effect - i.e., the 4MMP gets bound during the boil before it can flash off.
Furthermore, they also indicate that copper binds 4MMP. So, if you use a copper wort chiller that is another mechanism where you may possibly end up with more
4MMP in your finished beer by boiling it compared to steeping it, if it turns out that the bound 4MMP has less affinity for copper.
Regardless, we taste with our tongues and not an HPLC. The chemistry here is complicated enough where sensory analysis will continue to trump chemical analysis for quite some time, I'm sure.