I use the IGI on FamilySearch a lot, but usually only the 'Community indexed' section - I do not trust the 'Community contributed' section at all.
They also had a nasty habit of assuming that a man was aged 25 when he married, and a woman was 21, and 'calculating' a date of birth from this. They also assumed that someone was 'of' the place where they got married, oblivious to the fact that in Scotland, someone who is 'of xxx' is the landowner of xxx, not just someone who happens to have lived there.
I think the IGI is a wonderful tool, for all its many drawbacks (not 100% coverage of available records, curious spellings, assumptions, out of date) and sometimes one of the trees there contains a useful hint or two to be followed up. But FamilySearch mostly has just indexes and transcriptions, not original documents, and it is always essential to check the originals. Even then, be careful - witness the incorrect name of David Winchester's father on his first marriage certificate.
I repeat, with emphasis: never, ever trust anything you find online unless it's an image of an original documents, and even then be wary.
Do not, for instance, take as gospel anything I have said. Go and get the original documents and check for yourself.