The heart of your trading system
In my opinion Yield Curves are at the heart of any trading systems. Generally Yield Curves are used to discounting of forward values and estimate future payments. Furthermore Yield Curves are used to estimate credit risk, forex products, repos etc. There are many types whose setup depend on what they are used for. All instrument classes use at least one Yield Curve for calculating the present value.
The basic curves are the curves used to discounting and forward rare estimations. Other Yield Curve types use the basic curves as the basis. In other words all your Yield Curves are not better than the basic ones. Valuation, P/L estimations all greeks, dividend estimations etc. are more or less affected by the factors from Yield Curves.
Yield Curves obviously don't come from nothing. Building Yield Curves demands knowledge of the benchmark instruments and the money market for the actual currency. That is, an understanding of the fact that e.g. Yield Curves for AUD are built completely differently to – say – SEK Yield Curves.
How important are Yield Curves anyway? All financial instruments are valuated to their present value. That is Warrants, Options, CDS and many more asset classes are also affected. Money Market products like FRAs, Swaps, FRN etc. are highly dependent on the right Yield Curve setup. The pricing, P/L, hedging depend on those Yield Curves, their values are no better than your Yield Curve setup.
Don’t even think about customized cash flows, no plain vanilla products, exotic, Constant Maturity Swaps or any pricing which is not vanilla if your Yield Curve setup is wrong.