I see a lot of people here claiming steam buffer tanks are completely unnecessary for nuclear reactors since 2.0, but from my own testing, I found that, that is not completely correct.
Only reading reactor temperature and fuel, and having no buffer, can create outages in extremely high demand situations, due to the exchangers consuming the heat too fast, and the reactors not heating up fast enough because they're on a fuel diet. Of course, you could counteract this by having the temperature threshold be something fairly high (like 700+ degrees), but that then creates a problem of over consuming fuel during low demand.
I found that steam buffer tanks solve this problem: you can insert fuel on a very strict schedule of temperature <500 degrees, but open an exception to insert indiscriminately when the steam buffer gets below a certain point. This way, you get the best of both worlds: 100% fuel efficiency, and capability to actually use 100% of the reactors, if needed.
Of course, this is only an optimization that makes sense when you consider these edge cases, but still cool to think about, imo.