Source-to-pay is the full chain from requirement to payment — the combination of source-to-contract and procure-to-pay.
Two sub-chains. S2C: requirement to contract signature. P2P: order to payment.
Why it matters. A break between S2C and P2P causes leakage.
Market reality. Many suites grew out of their P2P side, with greater depth there than on S2C.
Selection criterion. Evaluate S2C depth on its own merits for services-heavy spend.