I guess I do mean mixing the poses.  Yep, I've done that as well, but I've also made sequences and saved various partial poses sets - using 'Select Subset' - when saving the pose file, and adding those partial pose sets to other animated sequences.  Using subsets allows mixing animated elements to make variations, etc.

If you have a good walk sequence, or any pose sequence that controls hips and legs, it's nice to be able to add that to whatever arms and hand poses you have might also have.  Making sets that mix and match can be fun.

But yes, when I said mixing splines I guess I did mean animation elements and should have said poses.