Assuming that the automatic customization at the global level was done when AUC TeX was installed, your choice are now. Will you use it? If you use it, you will benefit by having access to all the symbols and environments available for completion purposes. The drawback is slower load time when you edit a new file and perhaps too many confusing symbols when you try to do a completion.
You can disable the automatic generated global style hooks by setting
TeX-auto-global to nil.
User Option: TeX-macro-global
Directories containing the sites TeX style files.
User Option: TeX-style-global
Directory containing hand generated TeX information. Must end with a slash.
These correspond to TeX macros shared by all users of a site.
User Option: TeX-auto-global
Directory containing automatically generated information.
For storing automatic extracted information about the TeX macros shared by all users of a site.