Why a branch is taxable
Article 11 makes a non-resident person a taxable person if it has a permanent establishment in the UAE. Article 14 defines a permanent establishment as a fixed or permanent place in the UAE through which the foreign business is conducted, or a person who habitually concludes contracts in the UAE on its behalf.
A licensed branch with an office, staff and local customers clearly meets that test. So, in some cases, can a foreign company without a branch licence whose UAE sales agent habitually signs contracts for it.