The mitzva of safeguarding the matzot was stated with respect to the matzat mitzva we are commanded to eat on the night of the 15th of Nisan. The idea is to honor the mitzva by guarding them especially carefully. In other words, it is permitted to eat matzot that were not guarded if there is no concern that they may have become ḥametz, but they are not fit for use as matzot mitzva since they were not safeguarded especially carefully for sake of matzat mitzva. Accordingly, throughout Pesaḥ, one may eat non-shemura matza that is kosher for Pesaḥ.
Nevertheless, some are meticulous about eating shemura matza throughout Pesaḥ. There are two reasons for this: One is that some poskim maintain that while there is no duty to eat matzot throughout Pesaḥ, one who does so fulfills a mitzva; therefore, one should eat shemura matza (as explained in section 1). It follows that one who wishes to fulfill a mitzva by eating matza must eat shemura matza. However, according to this view, it is sufficient to eat a kezayit of shemura matza at each meal. Similarly, it is enough to use our regular matzot (not labeled as shemura), which have been safeguarded from the time of milling, because, as we have learned (section 2), one technically fulfills the requirement for matzat mitzva with matza that has been guarded from the time of milling.
The second reason is concern about ḥametz. Out of all the foods we eat on Pesaḥ, matza is the likeliest to become ḥametz. Therefore, if the wheat grains are not guarded from harvest time, there is concern that some wheat kernels may have become ḥametz. Thus, there are grounds for the scrupulous practice of eating matza that has been safeguarded from harvest time throughout Pesaḥ.
Today, the advantage of matzot that have been guarded from harvest time is not only in their having been protected from contact with water since the grain was harvested. In general, much more care is taken throughout their entire manufacturing process. For example, the baking machines are stopped every 18 minutes for a thorough cleaning. Thus these matzot benefit from a whole series of enhancements.
In sum, regular matzot, which have been guarded from the time of the milling, are kosher for all of Pesaḥ, le-khatḥila. Even those who maintain that there is a mitzva to eat matza throughout the seven days of Pesaḥ agree that one fulfills the mitzva with such matzot. Those who are more scrupulous eat matzot that have been guarded from harvest time, because these matzot are more carefully safeguarded from becoming ḥametz.
It thus emerges that the primary enhancement of the mitzva is to guard the wheat against becoming ḥametz from the time of harvesting. Thus, the kernels are harvested before they dry out to prevent any concerns of rainwater potentially making them ḥametz. The kernels are then stored in a dry place, preventing any kernels from puffing up or splitting, which would indicate that they have started to become ḥametz. On the other hand, wheat imported from abroad, from which all other matza is made, sometimes contains kernels that have already become ḥametz. Even though matza bakers are careful to purchase clean shipments, there is still a concern that some ḥametz kernels mixed in. And even though these kernels are batel be-shishim (because the matza is baked before Pesaḥ, according to most poskim the ḥametz is not ḥozer ve-ne’or on Pesaḥ, as explained above, 7:3-4), this matza is not as optimal. Since matza that was guarded from the time of harvesting is more optimal, bakers are careful to perform all of the other steps in the most meticulous way possible: during baking, they stop the machines every 18 minutes and clean them thoroughly; they constantly declare that they are working le-shem matzat mitzva; and they are more careful to supervise the entire process. Conversely, the trend with regard to non-shemura matza is to produce and sell it as cheaply as possible, so that the general public will be able to afford it. Therefore, only the mixers used for kneading are changed every 18 minutes, but the rollers are cleaned while they are running. Although they are cleaned in a way that ensures that every part is cleaned every 18 minutes, since the cleaning is done while the machines are running, it is more difficult to clean the machines thoroughly.
Yet shemura matza is far more expensive than the regular matza (even if it is only guarded from the time of milling the wheat and can thus be used to fulfill the mitzva of eating matza according to those who maintain that there is a mitzva for the entire holiday). Some say that it is preferable to give charity to the poor or to support Torah study than to buy shemura matza. On the other hand, why shouldn’t one who spends lavishly on furniture, clothing, and other luxuries spend extra money to fulfill mitzvot in the best possible way? Ultimately, in practice, regular matza is kosher le-khatḥila, and one may rely on the fact that the kashrut supervisors do their jobs properly. When it comes to fulfilling higher standards of mitzvot, one must decide if and how he wishes to go beyond the letter of the law.