I can't understand why anyone would want to mix their own D76 when the original is available ready formulated. Should I try and make my own Leica?
A few reasons:
1. It's very inexpensive to mix your own, once you have an accurate scale (which is only a few tens of dollars) and the raw ingredients (hydroquinone, metol, sodium sulfite and borax, if I remember correctly). Particularly for those who prefer to mix small amounts at one time (two litres and under), the cost savings will be significant.
2. You can mix precisely the quantity you want. You are not limited to one litre or one US gallon (an awkward measurement for we metric workers) or five litres. Mix whatever amount you want.
3. The raw ingredients keep for years - nearly indefinitely - if properly stored, and proper storage is not onerous.
4. If you have a stock of raw chemicals, you are no longer at the mercy of your local shop's stock levels or the delays of mail order. (Even if you normally use packaged chemicals, this is a good reason to have raw chemicals.)
5. You can tweak the formula if you wish.
6. You can use the same ingredients (less hydroquinone and borax) to make D-23, which is an interesting developer unto itself. If you buy a small number of other chemicals, you can make many more developers including print developers.
7. There is a slight geeky coolness to being able to do it.
And to extend to why you might, in general, use bulk chemicals (perhaps a new thread is in order if people want to talk about this):
8. Photographic chemical companies come and go. If you have the formula for a chemical, you can make it yourself and are no longer dependent on that company's existence to procure the packaged chemical. (Ansco 130 is a great example of this - it's my favourite print developer but it hasn't been sold on the marketplace, aside from Photographer's Formulary's small kits, in decades.) I imagine D-76 will be the last developer standing if the market really contracts, but there are plenty of other developers (and other photochemicals) that will be gone that will still be viable through home chemistry.
I wouldn't build my own Leica - but a good analogy might be why I might make my own coffee or tea at home when I can go to a shop and they can make it for me. If you don't want the hassle, don't do it, but it has definite advantages.
We're talking easy stuff - measure, measure, measure, measure, add to warm water, stir, done. It's not that much harder than mixing up a package of D-76 from Kodak.