Each update incorporates any fixes and features from the previous updates. You can find them here:
You can now export any mesh as per-frame BIF files. For more information, see Cache meshes using BIF format.
The behavior of BOSS caches has been improved. Now when you save a cache using tokens such as <project>, <scene>, or <object> in the Cache Folder and Cache Name attributes, a copy of the fully resolved path is also stored in the scene and used for playing the cache back. This means that the path to the cache is not lost if you save the scene under a new name or in a different project. If you later rewrite the cache files, the current values of the tokens are used and the resolved path is updated.
By default, there is a new preset rule in the Color Management preferences. The tx rule assigns files with an extension of .tx to the Raw input color space. Like the other preset rules, it is not available if you have previously saved preferences for Maya 2017.
For information regarding new API features in Maya 2017 Update 4, see What's New in API in Maya Update 4.