Photoshop
If a house is under construction, there is a point where there is enough information in a photo to create a rendering without having to start a drawing from the very beginning. It is also nice to be able to add landscaping, remove new window labels, or experiment with possible color schemes.
Exploring color choices

AS IS: Beautiful new stable, owner wanted to consider color options

OPTION: Stable, showing owner how their alternative color would look.
Planning and Zoning Proposal Presentation

AS IS: Derelict house in mixed-use neighborhood

PROPOSED: Light industrial building with planned parking and landscaping.
Poor photo lighting, dull time of year.

BEFORE: Backlit house in wintertime: Landscaping is hard to see, colors are subdued

AFTER: Brighter, cleaner in an illustrative style that signifies it is a new construction.
Finishing the house, adding landscaping and fencing

BEFORE: Unfinished house, no landscaping, exterior lights, or grass yet.

AFTER: Showing it finished, as it will look by the time the advertising is seen.
Finishing the house, changing the season

BEFORE: Unfinished house in wintertime: Colors are subdued, no landscaping, shutters, exterior lights of grass.

AFTER: Brighter, cleaner, showing it finished look in springtime.