When creating a category how important is it to have a new title to sell into? Can you create a category with an existing role as main user?

Not critical. In fact, you may be better off launching a new category into an existing (and much larger TAM) than also taking the task of creating / expanding a smaller TAM. The work that Gong and Drift are doing within the sales and marketing community (respectively) is quite impressive.

The catch is that owning a niche can lead to some great business outcomes for the company on top. 

When it comes to category creation, the idea is to position and evangelize a new problem that's observed in the marketplace for the very first time -- regardless of whether or not the title you're selling into is new or existing. More on that here. 

I don’t think it’s super critical for there to be a “new role” when creating a new category. When I was at Yammer, for example, we defined the “Enterprise Social Networking” category but made it a must have for various existing roles in an organization (VP HR, COO, VP Sales, etc.).

What you’ll find is that new categories often don’t have a corresponding line item in the buyer’s budget - so you’ll need to help them identify ways to fund the spend for your solution (by borrowing from other line items or creating new budget entirely).

You can create a category either way, but either way it isn't easy!

Gainsight is a great example of a company that created a category by building a platform for, and championing, a new role that had emerged - the Customer Success leader. This was fueled by a shift to subscription-based billing, where retention became a primary growth lever for SaaS companies, and the Customer Success leader the person responsible for driving it.

But you can also look at the creation of the Marketing Automation category, sold to marketers, a role that has essentially existed for hundreds of years. What's interesting here is that the Marketing Ops role (and team) grew in stature from this, as traditional marketers weren't equipped to deal with the advancing technology. 

More important than whether it's a new or existing role you're creating a category for is finding a new and unique way to solve a really big problem that exists for either. Obviously, if you have a new role you are selling into, there will likely be fewer solutions to compete against. So there's that.

My last thought on the topic is that there are way too many early stage companies out there trying to create categories out of niche solutions trying to solve a narrow problem. That seems really hard if not impossible.