Absolutely not. But of course you can use it if you prefer, see Can I use my own carrier contract with pre-negotiated rates?.
The label platforms we integrate with have ready-to-use contracts for a variety of carriers:
See here for a list of all carriers: https://goshippo.com/carriers/
Ready-to-use discounted rates for:
DHL Express (US outbound)
Deutsche Post (Germany)
See here for a list of all carriers: https://www.shipstation.com/partners/integration/carriers/
Ready-to-use discounted rates for