The intent of Promotional is to hide the (official) release from the discography:

https://tickets.metabrainz.org/browse/MBS-7181

Currently, https://musicbrainz.org/doc/Release#Status says,

promotion

A give-away release or a release intended to promote an upcoming official release (e.g. pre-release versions, releases included with a magazine, versions supplied to radio DJs for air-play).

I would recommend the following changes:

1. Explicitly add "sampler" to the promotion status.
2. Explicitly mention that the purpose of the status is to hide release groups that are "clutter".
3. Remove "releases included with a magazine" because it is often the case that this is the only way that the record company sanctions you to officially buy the music in question.  For example, in Japan, many music discs only exist as a disc inside a video product - these discs might say "no renting", but they do NOT say "for promotional use" nor "not for sale".  A reasonble person would not consider such an official soundtrack to be "clutter" that should be hidden from the default discography.  Many official soundtracks are only bundled inside video products or other non-music products, and that makes them a poor fit for MusicBrainz's intent for the Promotion status.

In other words,

A release intended to promote an upcoming official release (e.g. pre-release versions, samplers, versions supplied to radio DJs for air-play). This status is intended for officially sanctioned products whose release group would be deemed to clutter the default discography view.