Such devices are useful for removing solvent or dehydrating samples.
They are equivalent to Abderhalden's drying pistol in some ways, but vacuum ovens typically can accommodate large samples.
A characteristic operation for a vacuum oven is the activation or regeneration of molecular sieves.
[1][2] Vacuum furnaces are related devices that operate at much higher temperatures and much lower pressures.
The acetylacetonate complex Mn(acac)2 is obtained by vacuum drying the yellow dihydrate Mn(acac)2(H2O)2.