Let's jump right in! When I sit with my natural hair clients they are familiar with the advice to trim their hair 3-4 times a year. Even if they like that advice or not. It's what most hairstylist will suggest. Especially, when heat is applied to the hair often. As far as locs go, many people will go years without a trim. Due to many trying to achieve that below waistline length.
Honestly, people with locs should trim their locs at least 1 time a year. If they color with lighter colors I suggest 2 times a year. Untrimmed locs for years will result in the locs deteriorating on its own. That's when you will see the locs start to break apart on the ends. Some may look to repair the locs. Which can be pricey and time consuming. Just do your annual trim. Your locs will thank you.
Another way to keep your locs/natural hair healthy is to keep it moisturized. I will highly suggest our Nubian Kinks hair oil. Any scent of your choice. I would apply 2-3 times a week. Or as an alternative, the Nubian Kinks Liquid Vitamins Spray.