A Fractional CTO helps you in quickly launching your MVP in “weeks” and not “months”, and creating some low-hanging revenue stream for the product and leaves room for quick future scaling, and saves you from going off-track. 
Fractional CTO for Early-Stage Startups
1. Understanding Your Product Idea and Long-Term Goal:
This is the first task essentially. The Fractional CTO understands what you want to create thoroughly, divide the total feature list of your product into “Regular features”, “Unique features”, “Complex Features” and goes to the next Step.
2. Help You Create the MVP Quickly:
A Fractional CTO will guide you to create a lean but useful MVP version of your product and launch within weeks and then put that into iteration for gaining more market.
3. Tech Stack Identification, Architecture Design, Building Technology and Product Development Roadmap:
Based on the specific demands of your product, a Fractional CTO will identify the Technical Stack to be used to achieve the goals and also considering the long term scalability of the product.
4. Guiding the Startup in Sourcing the Talent:
Depending upon the project needs and budget, a Fractional CTO may suggest you to either outsource the whole project to a proper Development Company like Agicent or to distribute different components of your product to different vendors.
5. Overseeing the Developmental Operations:
So they get involved in implementation as a Supervisor or a guide and review deliveries, give feedback to the team, help them with troubleshooting when needed.
Fractional CTO for Bigger Startups 
1- All or a Part of What a Fractional CTO Does in an Early Stage Startups:
2- More Strategic Involvement:
Assuming that a bigger or mature startup will have more Technical leaders and Project and Product Managers, the role of the Fractional CTO here would be more focused on creating short and long term Strategies related to product development and Technology as a whole.
3- Creating and Owning Distributed Development Teams:
The CTO will define which team does what, and also design their collaboration protocol, setup up KPIs and KRAs and oversees and makes sure the work is being done as expected.
4- Helping in Creating Partnerships and Profitable Collaborations With Other SAAS Providers or Tech Companies:
You need your Fractional CTO whenever you want to forge a tech Partnership with another technology provider or a SaaS provider. The CTO will help you getting a better revenue sharing deal here.
5- Team Transition:
A Fractional CTO will guide the process of Transition when you outsource all or a part of the work to an offshore team or vice versa when you bring back your outsourced work and create your own inhouse development team.
Source: https://www.agicent.com/fractional-cto