Process vs People
There's no magic bullet for organization in large structures.
One way is to have processes that describe how each part of the company must interact with other parts in a given context. This allows for a "silo" mode working: parts of the company don't need to talk much to each other given they execute their part of the process, and building and evolving the process is left to some overviewing authority, external to the activity itself.
Another possible organization is to put people in charge of a customer visible part of the activity, and to let the person choose how he or she wants to run the activity. This goes to how is IT managed.
Process are usually seen as the way to go from craftmanship to industrial grade production, whatever the business is, meaning at the core that some kind of design must be repeated without variation. You perfect the design on one hand, and since the design is then carried out without variation, or assumed to be so, the improvements in the design are replicated.
At the beginning of every product is some kind of craftmanship. Generally a small teams of very skilled people design a product and build a prototype. Then
One of the possible organizations is per workmanship (not very far from taylorism), I mean by that that every service is specialized by organ, not function. At the other end of the spectrum is per business lines.
Some basics functions for a product are, say, marketing (matching market need with company know how), design, build, sales, run (exploitation), and customer support. For every of these functions, you need some kind of IT support: CRM for your customers, web site and e-commerce for sales, may be some software to support business funnel tracking if you're in B2B, some specialized software for design, and so on.
Let's take the example of a telco. Certainly, you have at least two products (in real life, it's rather thousands, grouped by product line, but this is an example). For example, you have enterprise access, meaning you need people to build phone lines or fiber optic at your customer's premises, but you also need IT, both in design and running
Build vs buy
Internal vs external
Process vs result.
Consequence: no IT in the company, each department must choose and run it's own IT.