Every time that we treat the hair follicle the follicle gets weaker which causes the hair to become lighter and finer. Pretty much every time that we treat the hair you will be able to see some improvement in the texture and color of the hair.
Sometimes men do not want to be completely bare in a particular area- such as the chest, legs, arms- but they want the hair to look and feel thinner. Depending on the person, the area, the ethnic heritage, etc the amount of treatments may vary. Usually having 3-5 treatments on a non hormonal area will make a big difference. The exception is with a man's face which the treatments are great and helpful but the process is a much longer one (read the blog on lasering the man's face).
When you get the area treated the hair takes about 10 days to shed out. Once out it takes about 4-4 1/2 weeks to grow back. At that time the hair will be a little lighter and finer so some men feel after one or two treatments their hair is thinner and where they would like it to be but our body has the ability to heal and in most cases the healing benefit is great but for the damaged follicle from laser it is not helpful. So if you just get a few treatments and do not weaken the follicle a good amount the follicle will start to heal and the hair will start to thicken fairly soon. Once we damage the follicle a good amount (again roughly in 3-5 treatments) then the hair usually stays in that damaged state for a good deal of time- maybe a year or 2 or more. If the hair starts to thicken a bit after that time you can come back for one or two more treatments to weaken the follicle again.
With my husband we wanted to thin out his chest but not totally rid to of hairs. We performed around 4 treatments back to back- every 6 weeks- and the hair stayed thinner for a few years. Once the hair seemed to thicken a little we treated it one more time. Now we treat the area about once a year to keep it thinner.
And by going through this process the hair is much easier to shave and the shaving is much less irritating to the skin due to the hair being thinner.