This question or a form of it has come to my attention many times. People usually wonder about this when they learn that witnesses described Joseph translating by using the Interpreters or seer stone in a hat which was used to perhaps block out ambient light.
As far as we know, the plates simply sat on a table under a cloth the whole time. Joseph did not translate them in any kind of way that that would be familiar to us today.
Translation usually involves understanding the source language and rendering the meaning as best as one can in another language.
Naturally one might wonder why Joseph needed the plates in his possession at all. Why bury them for 1600 years and go through the trouble of etching down all that information if it would never be read by someone?
Many things come to mind, nothing definitive, but many theories. I’m not going to cover them here, but in 3 Nephi 27 are a great couple of verses that provide some essential insights:
Touch not the things which are sealed, for I will bring them forth in mine own due time; for I will show unto the children of men that I am able to do mine own work. Wherefore, when thou hast read the words which I have commanded thee, and obtained the witnesses which I have promised unto thee, then shalt thou seal up the book again, and hide it up unto me, that I may preserve the words which thou hast not read, until I shall see fit in mine own wisdom to reveal all things unto the children of men.3 Nephi 27:21-22
Basically, the plates have not yet served their entire purpose. A portion of them was sealed by the power of God and are currently unknown to us.
What Joseph translated was just the beginning, a very small portion of greater wisdom which is to come. In the brass plates version of Isaiah is the following verse that has been understood to mean the Book of Mormon:
…in the book [of Mormon] shall be a revelation from God, from the beginning of the world to the ending thereof.2 Nephi 27:7
There is a lot more coming, and we can prepare for it by receiving what the Lord has already given. Almost a millennia after Nephi, Mormon wrote these words from the Lord:
And when they [the Gentiles] shall have received this, which is expedient that they should have first, to try their faith, and if it shall so be that they shall believe these things then shall the greater things be made manifest unto them.3 Nephi 26:9
The answer is, no, the plates were not pointless to have. There are many unanswered questions as to what role they played in the translation process and the proximity to Joseph as he was translating. Maybe their presence for what Joseph was doing wasn’t important for the portion which he translated.
We do know that it was important for witnesses to see them in all their glory and that they still have much more information that will be revealed to us in the coming day.
Hopefully, they will one day sit in a museum in Zion for all to see and experience where many will be able to read the words that Nephi, Jacob, Mormon, Moroni, and others wrote with their own hands.