From the early reports from the Creator’s Update of the Xbox One dashboard it appears that the old “SNAP” mode is actually being completely removed. There are a number of titles that have achievements related to snapping the app or using snap mode in some form, and without snap mode these will be impossible to unlock.
The majority of these are from Xbox One apps so are not likely to be a huge concern to most people, but a couple of notable ones are in Threes! and the official TrueAchievements app.
Here’s the (probably incomplete) list of achievements that are affected: