Having an original document passed down through the generations can provide a firm foundation for the family historian. That is assuming you can find it, read it, work out what it is telling you and resolve any inconsistencies. In practice, considerable time and effort may be required to pull together multiple pieces of information from different sources.
For one set of my grandparents I have their wedding day certificate of marriage which shows the groom's father named as Charles Frederick Welch. Meanwhile, a cousin has the family's Holy Bible which I understand contains an inscription for the Family Register of Frederick Charles Welch and Fanny Welch, née Tipton. Well which was he? ... Charles Frederick or Frederick Charles?
It is clear from the registration of his birth that he was officially given the name Charles Frederick Joseph Welch. However, it seems that as a child and on into his marriage he was known as Frederick. For the records I have seen, the name Charles only reappears as his first name for the registration of his death and the certificate of his son's marriage which was a few months later. Meanwhile, the headstone placed on his grave still refers to him as Frederick.
Why register your son's name as Charles Frederick Joseph and then call him Frederick? Well it is worth noting from the birth certificate and census records that his father's name was Charles. The baby was named after his father. Perhaps the use of the name Frederick was just to avoid there being two people in the household who answered to the name of Charles!
As there was a census soon after his birth, we have evidence that the toddler was known as Frederick before he was two years old. What we may never know is whether the family started out calling him Charles and then changed over, or whether they always intended to refer to him as Frederick and passing on his father's name was only ever meant to be ceremonial.
The underlying question for a genealogist is whether you want to build up a catalogue of names and dates found in official records or aim to become more of a social historian uncovering richer details of lives as they were lived. The answer may influence which sources you go to consult, what details you seek to record and how much time you invest. However, there's always the option to avoid going around in circles, back-tracking from dead-ends, and instead read a blog which spotlights hints, tips and interesting anecdotes.