But first you need to understand a few things about hair and how it grows.
1. As hair grows long, it tapers...which means simply that it thins out as it gains length. Depending on a persons genes that thinning out is more or less noticeable. Everyone has a certain amount of taper.
Now before everyone freaks out and starts examining their hair - taper is not necessarily a bad thing, the word "thinning" just makes us think of balding old men...but it is not that kind of thinning.
Taper is caused by the hairs you shed and how long your Anagen (growth) Phase is. Many hairs on your head live until shoulder length, but around Midback it will already be less hair that has grown this far.
This quick skech shows what I mean:
Depending on how thick and heavy your hair is, it can be good to have some taper as it takes away some weight and a certain "drag".
But as we all know, noone wants to have so much taper that their ends dissappear, so I guess we can say that both extremes are not something you would want, but inbetween is all good depending on the look you are going for.
2. Layers are artificial, created taper, meant to make the hair fall differently, take some weight off, give some lift around the face or simply to create a different style. There is different types of layers but most commonly the front hair is shortened and the layers get longer further down the lengths. In some styles a "top layer" is cut, and most recently fashion has been thinning out hair with a razor to create a more natural tapered look (popular in Asia).
But - you may not like your layers, they have many fans but also many haters. I don't think you can generalize, it really depends on the person and what they want their hair to look like. But know this - layers can make it harder for you to grow out your hair since natural taper will be added to your already layered, thinned out hair. I used to have a ton of layers and I grew them out.
Left: That was my layered cut, already somewhat grown out but still very layered. Center: This is what the same cut looked like after having grown my hair without any trims. Right: That is the result after only a half year of monthly trims.
How does this work?
You have to keep in mind that when you trim, you don't simply only snip off 1/4 inch, your hair also grows down from on top. More even thickness grows down, while you trim at the bottom and in the end the thickness will meet in the middle.
That is also way more productive than just "cutting 8 inches" like most people would suggest, since you don't have to battle uneven growth and the shedding rate as much, you are in fact taking care of it monthly....not after 4 months. Take a look at the next skech, it shows heavily layered hair and the response to monthly trimming.