Design plans are pictures worth a thousand words. Gets everyone on the same page, leaving few questions to be asked.
A strong set of architectural plans communicates all aspects of a renovation even when no "major" changes exist. For instance, let's take a look at bathrooms: a strong set of architectural plans would depict the bathroom(s) and draw the elevations and ceiling. The plans would graphically depict material types, material extent, plumbing fixtures, lighting, outlets, etc. The plans would even describe the correct wall assembly behind tubs and showers, and how to waterproof them. From these plans, a GC would have very few questions, and even non-English speaking workers could easily see the intent. Lastly, the developer would have a single point of responsibility for the building's design, including the designer's specification of products, fixtures, and assemblies; should anything go wrong, the developer has one entity to talk to first.
This leads to my last point, and that is risk allocation. Developers playing "designer" unduly take on realms of expertise that they have no business taking on. Similarly, GC's can't fulfill the designer's role simply because they are executors (not creatives) that get the job done for a given budget. There is also a financial risk to a developer moving forward without drawings; what if he and the GC have differing opinions on the finish expectation, but, at the time of their contract execution it was not clear? Then, as construction moves forward, the developer starts asking questions? The GC pushes back, saying that he can't deliver the building at the developers expected finish level. A lawsuit results, and it comes down to a lack of clear direction. Once again, pictures are worth a thousand words, and building projects are simply indescribable using mere words.
It can be fiscally enticing to go forward without an architect, but it is not wise. Find the right one who gets development, and you'll find greater leverage in banking, construction, and sales.