One person working for multiple teams has its own pros and cons such as:
Pros:
It reduces artificial dependencies between projects.
Reduces induced administrativeand context switching overhead.
Increased domain knowledge and team cohesion.
It improves visibility and clarify on progress.

Cons:
Stagnation of technical skill sets.
Boredom and it’s morale problems.
Missing value of deep specialities.
Reduces opportunities to learn about other areas with developing a narrow perspective on the work.

From the abovementioned pros and cons it can be seen that working of one person in multiple teams can advantage the company or project but may cause disadvantage to that particular person in some or other ways.