I found the banns book very useful when looking for my great-grandparents marriage. I knew where he lived, and looked in the banns book for that parish. It gave me his future wifes name, which I already knew, and the parish where her banns were read. This was completely different from the parish I had expected to be because the family had moved house after the census of 1881. This was for 1886. I was then able to look at the marriage register for her marriage, and found the entry.
The banns book only gives the bride and grooms names and parishes. Marriage entry will give details of occupations of the couple, plus their respective partners, their ages, names of witnesses.
Early marriage registers used to have the banns entered and then the priest would fill the rest after the marriage, if he remembered!! Unfortunately the further you go back the less detail you get!!
I hope this helps.