Canning must without fail. It can not even be discussed. Any item after restoration (no matter how the restoration was complete-partial) must be preserved.
As correctly pointed out above, conservation of paintings held reversible varnish, lacquer that is easy to remove if necessary in the future.
The paint layer under the paint will inevitably-by-step to take (absorb) the dust from the air. If conservation is, the dust enters the lacquer film and dirt in the future be removed easily with a top layer of lacquer. Without the varnish film dust "eats" in the paint layer. And the dust - neizbzhna. And the collector's home and we have a restoration workshop and a museum on display.
That simple little illustration.
And the scheme is made up not of "old" painting, and in general for any oil /canvas. That is pollution from the air, I see everywhere. It is strange that you are considering without conservation is a mandatory part of the intervention in the work of art.
And pollution is everywhere and always, the only question the admissibility of their volume. Sorry for copyrights on the scheme - a necessary measure.