By Design: When the clip is edited and saved, the curves necessary to edit the clip are generated and saved to disk. Those curves have no bearing on the final size of the clip in a release build.

Steps to reproduce:
1. Download and open the attached project
2. Duplicate the animation clip from the model
3. Observe file size of the new animation clip(~200 kb)
4. Add the model to the scene
5. Replace the inbuilt animation clip with the duplicated animation clip
6. Record new keyframes on the clip (e.g. set scale of a bone)
7. Save the project
8. Check the animation clip size again

Expected result: file size is relatively the same
Actual result: file size increased by 3 to 4 times

Reproduced on 2017.2.3f1, 2017.4.3f1, 2018.1.8f1, 2018.2.0f1, 2018.3.0a1