This is probably well-known by many, but it may be a surprise to some to find out how much extra information you can get by looking at original documents.
Take an example of the UK 1871 census for Jane Blyth (Blyth-1017). The Find My Past transcription tells us that Jane is 20, a servant in the house of Robert Entwistle, and she was born in Middlesex, England. The house address is given as Commercial Street (Commercial Tavern), Christ Church Spitalfields, Whitechapel, London & Middlesex, England.
When I looked at the original record on Find My Past, I found this extra information: she was unmarried, a barmaid, and born in Stepney, Middlesex. Those extra facts can make all the difference in identifying a person!
Another document that can yield extra information is a marriage record, typically a church record. In the UK this will often give the bride and groom's fathers' names, and their occupations. And very often you will see the names of witnesses.