One way that animated feature films are different than VFX is schedules. Typically, an animated feature from Disney or Pixar will take 4-5 years from start to finish, and everything you see in the movie will need to be created and rendered from scratch.
VFX schedules are usually significantly more compressed, typically 6-12 months, so often times it is cheaper and faster to throw more compute power at a problem rather than paying a group of highly knowledgeable rendering engineers and technical artists to optimize it (although, VFX houses will still employ rendering engineers and technical artists that know about optimization). Pixar has a dedicated group of people called Lightspeed technical artists whose sole job is to optimize scenes so that they can be rendered and re-rendered faster.
Historically, Pixar is also notorious for not doing a lot of "post-work" to their rendered images (although they are slowly starting to embrace it on their most recent films). In other words, what you see on film is very close to what was produced by the renderer. In VFX, to save time, you often render different layers of the image separately and then composite them later in a software package like Nuke. Doing compositing later allows you to fix mistakes, or make adjustments in a faster way than completely re-rendering the entire frame.
VFX schedules are usually significantly more compressed, typically 6-12 months, so often times it is cheaper and faster to throw more compute power at a problem rather than paying a group of highly knowledgeable rendering engineers and technical artists to optimize it (although, VFX houses will still employ rendering engineers and technical artists that know about optimization). Pixar has a dedicated group of people called Lightspeed technical artists whose sole job is to optimize scenes so that they can be rendered and re-rendered faster.
Historically, Pixar is also notorious for not doing a lot of "post-work" to their rendered images (although they are slowly starting to embrace it on their most recent films). In other words, what you see on film is very close to what was produced by the renderer. In VFX, to save time, you often render different layers of the image separately and then composite them later in a software package like Nuke. Doing compositing later allows you to fix mistakes, or make adjustments in a faster way than completely re-rendering the entire frame.