When I started working at Pixar in Sept 2000, I only animated with stepped keyframes, breakdowns and liner inbetweening because that is how I learned to animated at Disney. Pixar is the KING of spline animation and this bothered a lot people (I was told as much.) Eventually, me and a few liked minded animators convinced the tools team to write x-sheet, a tool that let us record our held keyframes in our shot recordings and then move them for timing and push them back into the spline editor. It was incredibly efficient and fast. THE INCREDIBLES was the first film we used this widely and I think you can see the results. Eventually, many of us landed on a workflow that was held keys/breakdowns for blocking and spline inbetweening for polish.