Build vs. Buy refers to the philosophy and approach that organizations take when determining whether they should license existing software or “build” it themselves.
Some organizations with more robust engineering teams (and/or vendors) make a decision to build some of the pieces needed for personalization instead of buying them 100% off the shelf.
There are many reasons why building some (though generally not all) components makes sense, though there are also potential drawbacks
The specifications for the platform are exactly what is needed and with the exact systems you want to integrate with
Data ownership, usage, consent, and privacy can sometimes be more tightly managed
Time to value can be longer than off the shelf
Can be difficult and costly to maintain integrations w/ multiple changing APIs, etc.
Doesn’t have a common API language
The time to value is generally shorter
Integrations are often easier with many APIs and connectors “out of the box”
Requires less upkeep and maintenance costs
Less influence on the product roadmap and priorities
May or may not work with all of your internal systems “out of the box”
Switching costs between monolithic platforms can be considerable down the road