There are 11 advantages of Mettā (loving-kindness) said the Buddha in Mettanisamsa Sutta (the discourse of benefits of loving-kindness). The one who practice metta

1. sleeps in comfort
2. awakes in comfort
3. sees no evil dreams
4. dear to human beings
5. dear to non-human being
6. will be protected by gods (devas)
7. fire, poisons and swords can not touch him/her
8. his/her mind can concentrate quickly
9. his/her countenance is serene
10. dies without being confused in mind
11. if he/she fails to attain nirwana here and now, he/she will be reborn in brahma world

Complete sutta or the discourse can be seen in page 45 of the Book of Protection.