The gemara asks a strange question about whether wheat that falls from the sky can be used for the שתי הלחם that is brought on Shavuos. The gemara explains that the fundamental question is whether the requirement to bring the שתי הלחם from מושבותיכם means that it must be brought from produce of Eretz Yisroel, or is just to exclude using grain grown in chutz la'aretz. Meaning, grain that is not grown in E.Y. but is also not grown in chutz la'aretz would fall under this question. This gemara understood this question to be merely a theoretical, but nowadays is very practical. Hydroponics which is the ability to infuse water with nutrients that are typically found in the soil to provide a source from which the plant can draw it's nutrients, would seemingly qualify as produce not grown in E.Y. or chutz la'aretz.
Rashi and Tosafos try to explain the case of "wheat falling from the clouds". Rashi says that if a cloud would swallow a boat full of wheat and ascend, it could rain wheat. Tosafos doesn't take issue with that being a possibility, but says that if we are speaking about naturally grown wheat then the fact that it was brought up in a cloud shouldn't be relevant. Had it been wheat that was grown in E.Y. it would be usable for the shtei halechem, and if it was wheat grown in chutz la'aretz then it isn't usable. Therefore, Tosafos says that we are speaking of miracle wheat that initiated from the cloud and wasn't grown down on the land.
The Mitzpeh Eisan asks in the name of the minchas kohein that miracle wheat shouldn't be acceptable as a korban mincha because only food that is permitted to be eaten can be used - ממשקה ישראל - מן המותר לישראל, and miracle food is not allowed to be eaten like the gemara says in ta'anis that it is forbidden to benefit from something produced by a miracle? The Mitzpeh Eisan answers the question that the concept of not benefiting from a miracle isn't an issur, it is merely a middas chasidus. He then proceeds to prove from various places that there is no actual prohibition to benefit from a miracle, and therefore this wheat would be usable from the shtei halechem.
It seeems to me that the mitzpeh eisan may have overlooked a Rashi in ta'anis who writes this explicitly. The gemara in Ta'anis 24b speaks of a miracle where sand turns to flour, and on 25a speaks of a fire that is produced by a miracle that was used for havdala. Rashi 24b writes -
אמר להו מעשה נסים הוא, ובמה דאפשר להתרחק ממעשה נסים יותר טוב ונכון
Rashi clearly writes that the idea of not benefiting from ma'aseh nissim is "proper" but certainly not an issur. Regarding the use of fire produced by a miracle for havdala, rashi says that they lit another candle from that one therefore it wasn't considered using the fire of a miracle. It isn't so clear why rashi has to say that unless he holds that one must actually derive benefit from the havdala candle (we usually assume that we don't need to benefit but we show that we are able to benefit from the light).