We've all heard often enough that we shouldn't be satisfied with just finding an entry in the IGI (or on Familysearch, as they now seem to prefer to be called), but should actually go and check the relevant parish register or Bishop's Transcript. Here are a couple of real-life examples of why it really is important that you do so.
1. Familysearch shows me the baptism of Mary Ann Bell, daughter of Charles Bell & Ann Stewart, on 23 Jan 1809 in Newburn, Northumberland. It also says that she was born on 19 Feb 1809. However, when I look at the Bishop's Transcript for Newburn (available as images on Familysearch) I get the additional information that she is "1st daughter of Charles Bell, pitman, native of this parish by his wife Ann Stewart native of St Nicholas Newcastle-Tyne". Some parishes contain even more information, such as with the baptism on 10 Dec 1809 in Cockfield, Co. Durham, of Margaret Parkin "born March 26 bap Dec 10 1809, 7th d[aughte]r [of] Geo Parkin Pitman by his wife Anne d[aughte]r [of ] James Hodgson, Mason, Na[tive of]: Staindrop". In one step you not only have the father's occupation, the mother, her maiden name and where she is from, but also the name of her father. This information is not shown in the extracted information in Familysearch.
2. I found the marriage of my husband's ancestor, Stephen Breaks (or Briggs) to Ann Daglish on 2 May 1778 in Tanfield, Co. Durham. I looked in Familysearch and found an Anne Daglish, baptised 6 Nov 1737, the daughter of George Daglish. This would make her 31 when she married, but that seemed feasible. With the help of Familysearch I built up the following little family
George Daglish m Mary Fairlee or Fairlace 9 Nov 1735 in Tanfield. They had the following children:1. Ann Daglish bap 6 Nov 1737
2. James Daglish bap 3 Dec 1739
3. George Daglish bap 17 May 1741.
Looks great, doesn't it. But the problem came when I checked the Bishop's Transcripts. Ann (my Ann, as I had thought), was buried on 5 Sep 1741. That meant she couldn't have gone on to marry Stephen Breaks in 1778.
This is one of the big dangers of the IGI in that it rarely shows deaths or burials. How many others are chasing the wrong tree because they never checked the original parish register or BT?
Incidentally, I've never managed to find the right Ann Daglish, but I'll keep looking...