This entirely depends on the sub-floor material. For example, replacing the subfloor after removing tiles isn't necessary if the subfloor is made of concrete. However, if the subfloor is ply or yellow-tongue chipboard then repairs or replacement may be required. If the subfloor has minimal damage and remains level, you can install new flooring directly onto it. If the subfloor is warped, cracked, or uneven, replacing it ensures a stable and long-lasting floor.