Integrating HubSpot means keeping its contacts, companies and deals consistent with the ERP, accounting, email and support tools that hold the rest of the customer picture. Typical connections turn closed-won deals into orders or invoices, push financial status back onto the deal, and sync lists or tickets. What breaks is matching, because HubSpot dedupes on email and domain while other systems use their own keys, plus consent handling and rate limits on both ends.
HubSpot often runs marketing, the sales pipeline and sometimes service in one place. The rest of the customer picture lives in other systems, and HubSpot has to stay in agreement with them.
The most valuable connection is usually the ERP or accounting system. A closed-won deal becomes a sales order or an invoice, and order, delivery and payment status flow back onto the deal, as in SAP S/4HANA to HubSpot or Xero to HubSpot. The second group is other front-office tools: a CRM another team runs, an email platform, or a support desk such as Zendesk. There the job is keeping one person and one company, not two, across systems with different ideas of identity and consent.
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