In a typical conservation or archival frame job, the main objective is keep acid-bearing materials out of direct contact with the artwork. Untreated acid-bearing materials can seep acid which, when in contact with artwork, leaves a brown hazy effect called acid burn. Acid burn is a stain that permanently damages and devalues artwork. Materials used in conservation and archival framing are acid free for the express purpose of safeguarding artwork so it retains its value.
It stands to reason, therefore, that any mounting technique that might cause artwork to lose its value would also be off the table. Bearing this in mind, the process of coating a piece of artwork with adhesive and permanently sticking it down would not be considered archival, since sticking anything permanently to anything else tends to devalue it. For this reason the first method of mounting, called permanent mounting, should only be used for artwork unlikely to increase in value over time.