There is no such thing as a "perfect diet". Eating a variety of healthy foods yields the most benefit, but it is nearly impossible to get in all the necessary nutrients through diet alone. One of the most important nutrients we should take in is healthy fats, namely from Omega-3 fish oil.
There are a host of benefits from taking in fish oil such as:
1. Improved insulin sensitivity
2. Improved blood circulation
3. Reduced inflammation
4. Improved brain function
In order to get in enough fish oil through diet alone would be expensive and extremely hard to do. To supplement is cost effective. Shoot for taking in 2-5 grams per day of fish oil and reap the benefits!