Finding a planet that you want to find, is mostly luck, after knowing what settings you need to pick. Cold temperatures tend to knock most toxic gasses out of the air, but the same goes for non-toxic ones as well. So, atmospheres will be thin if you want them to be less likely to carry undesirable gasses. Another factor is Life in SE is assumed to boost Oxygen levels. I don't think Exotic Life does this. It might produce a different gas. How Earth's atmosphere became what it is today, included the work done by CO2 and O2 producing life, but that's a whole 'nother topic. The Creation and Evolution of Primordial Earth's Atmosphere would be a good thread! Yes, I tend to agree this thread should be about what SE is capable of doing with random generations. A thread about creating your own atmospheres would be more than welcomed, it would be a huge resource for everyone!
Anyway, being in the right place is more than half the battle, i.e. luck. In my experience, it seems these procedurally generated Galaxies have Star populations that are congruent somehow, and in their compositions perhaps too. I might find pockets of numerous Blue Giants in one place, or even more Terras in one part of the Galaxy. I might be imagining that too. The algorithms should have some noticeable patterns I would think. So, that means some areas of a Galaxy would normally be thin with certain planet types, again all speculative conjecture at 2am on my part.
Today was a lucky day. The first search I did from a random Black Hole, which I like to use as buoys or markers as I plot my way across a Galaxy, with a 1000 light year radius. No other settings where selected. It found 9917 stars out of a possible 10000. The first star I clicked on showed me this planet:
What's nice about this one is the toxic gasses are down at normal Earth levels. You couldn't even smell the H2S, and barely smell the SO2. The temperature is a very very comfortable 10 C, however the air is too thin at .00356atm. You would need to boost the total pressure 50 times over. Then the O2 would be right at Everest Death Zone levels and the CO2 would be tolerable for a couple of hours, but then the toxic gasses would also be up to levels too high to tolerate.
Blearg! OK, so I had to set some settings for another search. I picked, Cold Desert with any life, any biome and an atmosphere within Human preferences (.2 to 1.5atm in this case, I might enlarge that window both directions during other searches). Ah, well looky there, the second planet I found; Oxygen partial pressures the same as 3000m altitude on Earth & inspired O2 is lower than 60%, very good. CO2 levels are the same as the worst days ever, in Earth's urban and industrial centers (nearly deadly), but we have some wiggle room up in them thar hills. No SO2 around at all and you couldn't even smell the H2S. Ah, poop! it's -107 C! I grew up down south, and wouldn't like that one bit!
Again we are in luck! Since this is a moon around a Gas Giant, around circumbinary Stars too, there is alot of internal heat from all the friction of tidal forces, creating volcanoes! You would finally have a place to wiggle your toes by the fire, have fun looking up at a honking Gas Giant all night and wake up to a double Sun Rise, without wearing protection. Breathing mask I mean. Radiation might still fry your brain, so you'll have to accept all personal responsibility if you camp out under the stars at night on this new planet.
CPU: AMD FX-8350 8 core processor 4GHz / GPU: GeForce GT 730 @ 1920x1080, 60Hz with 1GB adapter RAM / RAM: Patriot Signature 4GB 1600MHz 240-Pin DDR3 (only 2GB work, don't buy it) / Motherboard: MSI 970 Gaming MS-7693