2.18A developer question you're likely to get

Interviewer:

Why don't you just query Salesforce first and determine whether to create or update?

You can say:

“If the source system provides a reliable external identifier and Salesforce has that field configured appropriately, I'd normally prefer upsert. It reduces the round trip, eliminates explicit query/create/update branching, and helps make retries idempotent.”

Excellent answer.

Instead of:

Query
 ↓
Choice
 ├─ found → Update
 └─ missing → Create

you get:

Upsert

MuleSoft itself describes Upsert as creating or updating based on a custom identifier and recommends it in many situations to avoid duplicate records.