Everything to do with how you heal. Remodelling of scars is a long process.
Generally it is recommended to treat once every 3 months. While you may heal on the surface within a week or two, deeper changes take longer.

For reading you can check out the FAQ; read about wound healing (inflammation, proliferation, neocollagenesis)

Some may see good results with just one treatment, for some it may take 3-9 sessions.

@Tdayton89Every 3 months treatment is needed it's a slow process to build collagen. Collagen is produced slowly. It's a individualized response - depending on how your body heals and responds. Best to wear sunscreen. Some wear a tinted moisturizer or tinted sunscreen to hide some of the redness or there is something like dermablend to conceal the area. You do not want to exfoliate or irritate these area or they can take longer to heal.

How many are needed between 3-8 sessions depending on the severity of your scars, your practioners skill, and the technique used.

The variability of treatment is up to your scar beds ability to raise from treatment.

Manual methods are always best first before energy devices are used.