The short answer: Almost all.
First-time founder's can benefit most
An incubator program is designed to help you flesh out your ideas, ensure you have a suitable business plan in place, and help you see the potential issues ahead and how to overcome them. This is useful for all founders, but particularly first-time founders.
Have a goal
When applying to an incubator, it’s important to have started thinking about what you know and what you don’t know. Much like higher education, there should be a goal in mind. Of course, it is possible to join and bounce around and slowly learn, but if there is a target it will be much more effective. The mentors, coaches, and business support can target their advice and recommendations.
Incubators often are associated with government, universities, or other startup foundations that may cover the costs, meaning you have access to a free program of learning. They may provide physical office space, and while some individual programs may be cohort-based, they often have rolling admissions.
It takes more than just a good product or service for a startup to be successful. The business plan, expansion plan, marketing, etc., all need to aligned and effective. Incubator programs are a way to learn for coaches and mentors who have experience with successful startups. They will often have knowledge and access to potential strategic partners to help expand your network, access to other training programs, and resources from universities.
If you have an MVP, a validated business model, or more experience, an incubator may not be the best use of your time. Instead consider an accelerator, a program that does exactly what its name says, it accelerates your growth with a much more intense program.