The blood knots in your hand-made leader butt, taper sections will never fail before your tippet knot unless you tie them so badly they defy simple physics i.e. big fat line knots are stronger than skinny tippet knots. Kind of hard to defy that but I guess it's possible. Furthermore the weakest point is usually the terminal knot (at the fly), and if you are still using a clinch definitely so.
So once you replace a tippet, it's safe to say that the hand made leader is no weaker than the one-piece at 10% of the price (if that).
It allows you to use only sparse portions of flourocarbon (e.g. tippet only) which is not the best thing for the environment or the wallet.
But much more importantly, tying your own leaders teaches you a tremendous amount and makes you a better angler over time. Leader design affects casting, presentation and handling of fish. It teaches you to recognize the feedback you might otherwise ignore or miss, make corrections and improve.
That, in my opinion, is what makes one angler better than another - the number of iterations one has improved their technique based on recognition of the available feedback.
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