What benefits does iOS 16.1.2 have?

16.1.2 addresses 1 vulnerability:

About the security content of iOS 16.1.2 - Apple Support

WebKit

Available for: iPhone 8 and later

Impact: Processing maliciously crafted web content may lead to arbitrary code execution. Apple is aware of a report that this issue may have been actively exploited against versions of iOS released before iOS 15.1.

Description: A type confusion issue was addressed with improved state handling.

WebKit Bugzilla: 248266

CVE-2022-42856: Clément Lecigne of Google's Threat Analysis Group

Please see: About iOS 16 Updates - Apple Support

Not anywhere near the benefits of iOS 16.3.1 which is the current update.

All the gory details here: About iOS 16 Updates - Apple Support