The GP01 was built on various technologies pioneered by the One Year War-Era RX-78 (Gundam), and incorporates advances in many of these concepts and technologies.
While the RX-78 was highly adaptable owing to its high performance, the GP01 is designed to utilize changes in equipment to adapt to different situations.
The advantage of this concept means that the GP01 can adapt to meet the needs of deployment environments or specific client requirements. Unlike the the RX-78 project where cost was 'of no concern', the GP01 was designed to seek a realistic balance between production model and test model.
Though the GP01 itself is designed to be configured to a variety of mission types and duties, there was also an additional initiative to add external parts to greatly increase the defensive capability of the Mobile Suit.
This initiative had its genesis as an improved version of the RX-78's FSWS (Full armor System and Weapons System) plan, creating the 'Full Armor Zephyranthes'. Though the RX-78's FSWS system reamined a system tested in simulations (with some rumors stating that an actual test version was deployed), the idea of completely covering the exterior in a outer armor shell proved difficult, as it was found challenging to create a shell with enough durability and strength for practical use.
Because there was not a realistic way to attach the external parts to the body of the Mobile Suit, the external equipment parts would cause uneven stress loads on each other, so it was judged to be quicker and move effective to completely change the external armor parts, rather than using add-on parts.
The GP01 FSWS initiative was also scheduled to test leg mounted hover units that would later become standard equipment on many Mobile Suits, the hover units eventually ended up being tested separately, and while they eventually were realized on other Mobile Suits, the Full Armor system would be scrapped along with the premature cancellation of the GP01 project, and so the hover units were never utilized by the GP01.
Source: Master Archive Mobile Suit: RX-78GP01 Zephyranthes