Doing things different in CI builds

Say you have a large complex solution.

Building everything takes longer than you'd like. Especially when building as part of CI checks, such as for a gated merge.

To make the CI build faster, it can be tempting to have a filtered version of the solution that only builds 'the most important parts' or filters out some things that take the most time (and theoretically change least often).

When such a filter exists, it can be tempting for developers in a team to use the filtered version to do their work and make their changes. If it makes the CI faster, it can make their development build times faster too.

However, there's an unstated trade-off happening here:

Shortening the time to build on (as part of) the CI

creates 

A reliance on individual developers to check that their changes work correctly for the whole solution.

If you get it wrong, developers (mostly?) only work with a portion of the code base, and errors can be overlooked. These errors (including things like being able to build the whole solution) can then exist in the code base for unknown periods of time......