Does an organism that lives in another organism always negatively affect its vital functions?

No, an organism living in another organism does not always negatively affect its vital activity. The cohabitant can benefit the host by supplying nutrients (nitrogen-fixing nodule bacteria and legumes).

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.