I’ve been doing a lot of postcards lately, but not all of them are for mailing. Postcards are popular at trade shows, job fairs. Maybe it’s because they are so easy to get them printed on even a meager budget. Possibly it’s the smaller size that’s easier to hang on to at a show. Whatever the reason postcards can be a lot of fun.
Printers have cut costs on printing full color on both sides of a postcard by ganging up the jobs. They print a bunch of postcards together and then cut everything up into separate cards. The advantage of this is a huge cost saving. The disadvantage is no adjusting color on the press.
There is no margin of error with this kind of printing, you need an experienced designer that understands color profiles and management to set up your postcard files exactly how the printer specifies so your it comes out the way you expect.