Spectrum of options from "Zapier 2 clicks" to "FAANG-grade custom infrastructure". The choice is not binary — many companies use a hybrid. But there are thresholds where custom clearly wins or loses.
Where SaaS wins
- Standard workflows — Salesforce → Slack, Hubspot → Sheets, Stripe → Email. SaaS does this in 10 minutes.
- No dev capacity — one marketing person has to handle it. SaaS is realistic, custom would be a blocker.
- Prototyping — you are testing a hypothesis, scale is low. Build in Zapier/Make, when it works rebuild in custom.
- Low scale — <1k operations/month. SaaS pricing is below the threshold where custom makes sense.
- Many integrations with popular SaaS — Zapier has 5000 connectors. Custom has to write each one separately.
Where custom wins
- Scale — above ~10k operations/month SaaS pricing explodes. Custom infra cost drops per operation.
- Browser automation — no SaaS does production-grade Playwright with anti-bot. Only custom.
- Specialty integrations — your own CRM, ERP, internal API, banking portals — no SaaS connectors.
- Performance requirements — <5s latency, real-time processing, custom scheduling.
- Data privacy / compliance — data cannot flow through third-party SaaS (banking, healthcare, gov).
- AI integration — LLM with custom prompts, fine-tuning, RAG, multi-modal. SaaS hits a plateau.
- Long-term TCO — after 18-24 months custom typically amortizes the setup vs SaaS.
Hybrid approach
Most scale-up companies have a hybrid: SaaS for 80% of standard operations, custom for 20% strategic. Zapier handles "lead webhook → Slack notify", custom does "AI screening + multi-source enrichment + CRM push".
Important metric: cost per outcome, not cost per tool. SaaS can be cheaper per ticket but more expensive per business result when you need precision.