At its core, skeletal animation trades CPU power for huge RAM and file size savings and many additional benefits (both for technical flexibility and production pipeline).
Skeletal animation also has a lot of benefits (like the ones described by Shiu, and this website).
- Swapping out equips, custom characters and clothing, through its skin system.
and most other benefits that 3D game animation has:
- Arbitrarily stretchable framerates (poses refresh like 3D games, which can be at 30 or 60 or 120fps. Or you can limit and stagger pose and render updates of numerous but less important elements to buy performance back.).
- Programmatic control of poses like pointing a head or eyes to look at an object while the rest of your character moves normally, or aiming a gun at any angle, as in the Super Spineboy demo.
- Footing IK (for posing your character's feet more correctly on inclined floors in platformer games.
- Warping (FFD) and bending (Skinning/Weights) of images, which can also be programmatically controlled so you can have physics-controlled chains or cloth.
It's really up to you to decide what you want to do frame by frame and what you want to do skeletal. Some games combine both. If you're developing for powerful platforms like consoles or Windows/Mac, you can do a lot of frame-by-frame stuff and the platforms can handle it (ram wise) fine. Customers also expect games downloads there to be by the gigabyte and people have terabytes of disk space, so there's no problem if your file sizes are huge. Same can't be said for mobile.
Sometimes, frame-by-frame is harder to animate. Sometimes skeletal is harder to animate (for what you need).
It's really a technical/artistic decision to choose between FbF and skeletal.
But you definitely don't need to stick with just one. Pick whatever's fastest to make, or what looks best, for each specific thing or set of things. Whatever works for your game.
