Agisoft Metashape Photoscan - Orthophot from Mesh or Dem

 Usually we recommend to generate DEM from the dense cloud and use this surface as input for the orthomosaic generation, thus the meshing step can be skipped.

For very large areas most likely it wouldn't be possible to generate a single-block mesh, therefore the DEM is recommended for large areas covered.

Using Mesh surface may be reasonable for custom plane projections (like building facades, for example) or for small areas, when mesh surface produce more accurate results, for example, by the edges of the roofs.