The Torah commands "Ushamrtem es hamatzos", to guard matzah. Exactly what the parameters of this halacha are is not clear. The gemara in Pesachim quotes Rava as saying matzah needs shmira from the time of cutting the wheat for harvest (ketzira), while the opposing view holds that shmira from the time of kneading the dough (lisha) is sufficient. The simple pshat in the gemara, which is how the Rambam and RIF pasken, is that shmira is needed for the wheat to not turn into chameitz. However, Rashi writes that the shmira we are speaking of is shmira for the purpose of the mitzva of matzah, i.e. "lishma". What compelled Rashi to learn that way is another braysa that tells us that matzah baked by an aku"m is perfectly acceptable for eating during Pesach with the exception of the miztva of achilas matzah. The Rambam, lshitaso, does not cite this braysa l'halacha. The Rosh stakes out an interesting middle ground and argues for shmira from the time of grinding the wheat when it potentially could come in contact with water (the Rishonim were speaking of water wheel mills), which is not an option the gemara mentioned.
The upshot of all this is a chumra and kula for each approach. The chumra of Rashi is that you need shmira "lishma", which precludes a katan or aku"m from baking matzah, but the kula is you only need this for matzas mitzva. The Rambam's chumra is that you need shmira m'sha'as ketzira for all your matzah, but the kula is that a katan or aku"m can bake matzah.
For those who have the hakpadah for the Rambam's opinion of using only shmura matzah for all of Pesach, it seems to me (and I'm not anyone's posek) that aside from leil haseder, you would be fine using only machine matzah. According to Rashi you don't need shmura except leil haseder, and according to the Rambam you don't need lishma, so you have nothing to lose even if you hold a machine cannot bake "lishma". For the leil haseder, you would have to determine the status of machinary viz. "lishma" in order to be yotzei the shita of Rashi.