An index is intended to help you find an item of research reasonably quickly, and as with indexes to books, some are better than others. But by and large, all are better than none at all. Indexes for example can be for Birth, Marriage and Deaths (BMD), or for census’. But just please remember it is just an index, used as a tool to aid research.
A transcription is (usually) one person’s interpretation of an original item, the accuracy clearly depends on the care taken and the interest the
transcriber has in the subject. However it is useful in that it is usually a fair representation of the original, and can help a researcher decide
whether it is worth seeking out the original document, or whether he is on a false trail.
The ultimate aim of your research into your family history – genealogy is to prove your ancestry through an original document. So once you have searched the indexes and scanned the transcripts, please obtain a copy of the original document. It is essential to see a copy of the original document and to decide for themselves on its validity.
In broad terms Free BMD (freebmd), Ancestry, LDS familysearch and other websites are great time savers and their dedicated voluntary researches do a great job, but internet research does not take the place of genuine research. Mistakes do happen. I have personally found out that this is so. When the 1901 census for the UK was heralded in, I could not find, from the online database a certain ancestor of mine, yet found it in the local county archives some months later!
So find the family history – genealogy research on the ‘net’, use it as a tool – but get that original document!