Elf is undoubtedly a Christmas classic, but the 2003 film was low budget, and the idea of creating a lot of the visual effects in-camera had many senior people worried it couldn't work.
Given Will Ferrell is such a global name these days, I hadn't realized how low budget (in commercial terms) Elf had been. In this video, you can quickly see just how difficult some of the shots were to get, and that is largely due to the decision to make the film without using digital effects, so as not to age it. I can imagine it's rather hard to resist the most modern digital effects as they're always impressive at the time they're cutting edge, but they will indeed age a film like nothing else. Whereas, using physical tricks — like forced perspective — can last the test of time, as we've seen with films like Lord of the Rings.
One common thread I have noticed with films using difficult techniques is how it often requires one strong vision and that person to remain steadfast under pressure. For Elf, that seemed to be Director of Photography, Greg Gardener. After they spent full days building up scenes and then shooting them using forced perspective, only to find that at the end of the day they didn't get anything usable, Gardener came under pressure from the studio. Never the less, he knew what he was capable of and stuck to his guns, and the results speak for themselves. Elf grossed $220,000,000 and became a beloved Christmas classic, guaranteeing it a surge of seasonal revenue each year.