Practicality of Integrating CRM & ERP Questions – B2B SAAS

I’m doing some search regarding how CRMs are used from when SAAS B2B businesses start using CRMs to when they go IPO. There are a lot of high level articles, but nothing that actually goes into any significant detail.

When did your company decide to integrate your CRM with an ERP (Netsuite) or Billing tool (Zuora/Chargebee etc)? What were the main drivers? Examples: Self-service deal capture, use of managed package order form create or order processing?

Any common mistakes that you see? I've mainly seen the untrained people attempting to integrate, impractical ROI % goals and underestimating on-going management costs.