(→Acceptable reversions: advice to avoid edit warring)
The main purpose of reversion is to undo vandalism
In the case of a good faith edit, a reversion is appropriate when the reverter believes that the edit makes the article clearly worse and there is no element of the edit that is an improvement. This is often true of small edits. Edits that introduce [[wp:undue|undue weight]] should be reverted until consensus is built.