Benefits of TNR: https://www.alleycat.org/resources/why-trap-neuter-return-feral-cats-the-case-for-tnr/
Trap-Neuter-Return (TNR) is a humane method of trapping community cats to be spayed or neutered, vaccinated, and returned to their colonies to live out the remainder of their lives. TNR is the most humane and efficient way of controlling cat populations. It helps to reduce disease, overpopulation, noises and nuisance behaviors such as spraying and promotes better overall health of outdoor cat colonies.
After being spayed or neutered, cats tend to live longer, healthier lives. Spaying a female will prevent them from going into heat, which in turn reduces the amount of new tom cats coming to the area and helps to minimize fighting. Female cats can go in heat as early as 4 months.