From the Seattle Times:
The Obama-era rules were intended to avoid civilian casualties from drone strikes, commando raids (such as the Navy SEAL one in January), and other counterterrorism missions.
Three provinces in Yemen have already been declared an “area of active hostiles”, which was a status requested by the Pentagon and granted by the president. This declaration made possible the January Navy SEAL raid, which killed many Yemeni civilians including women and children.
Trump is also expected to sign off soon on a similar Pentagon proposal to designate parts of Somalia to be another such battlefield-style zone for 180 days, removing constraints on airstrikes and raids targeting people suspected of being extremists with the al-Qaida-linked group Al Shabab.
This is being considered a test run on whether or not to more broadly rescind the Obama-era rules.
Rescinding these rules will allow for an acceptance of more civilian casualties for the sake of carrying out more countterrorism missions.