When should you not self-host?

Do not self-host when nobody in the company will own the server, when a regulator or a contract requires a certified vendor, when the open-source option in that category is immature, or when your volumes are low enough that hosting and attention cost more than the subscription. Owning software is an operating commitment, and it only sometimes saves money.

Saying that plainly is part of doing this work honestly, including when it costs us the project.

What if nobody will operate it?

A running system needs updates, backups, monitoring and a person who answers when it breaks. Where that person does not exist and nobody wants the role, self-hosting turns a predictable bill into an unpredictable risk. A vendor's uptime commitment is worth paying for in that case.

What if a regulator requires a certified vendor?

Some contracts, audits and procurement processes name certifications, data-processing terms or vendor insurance that an open-source deployment on your own server cannot satisfy, even where the engineering is better. Compliance is a constraint on the design rather than a matter of taste.

Where regulated data is involved, the alternative is usually a private deployment rather than a public one, which is a different decision from open source versus SaaS. Agent isolation covers where that boundary sits.

What if the open-source option is immature?

Billing, payment processing and some compliance-heavy domains have no mature open-source product. Deploying a young project into a load-bearing role makes you its maintainer, which is a different commitment from using it.

What if the volumes are too small?

Below a certain usage, hosting and attention genuinely cost more than the subscription. A one-person business replacing a single seat with a server it has to maintain is making a worse trade, even with no licence fee to pay.

What if the process is not yours?

Where a tool does exactly what you need, needs no customisation and your data may live with the vendor, paying that vendor is rational. Rebuilding a commodity product badly is the most expensive form of ownership available.

What should you do instead?

Narrow it. Keep the commodity tools and own only the one or two systems your specific operations run through. That is the arrangement most of our clients end up with, and it is usually the cheaper one. Open-source business systems covers how that selection gets made.