There are few advantages and disadvantages of this technology.

Advantage

Similar to heat mapping which is used to increase conversions and augment sales, you can use eye tracking for the similar purpose.

They are useful for research purposes.

It can be very helpful before launching a product or app to see user engagement.

Disadvantage

Eye tracking softwares are new and hence more expensive to use.

They are still experimental.

They may be difficult to set up.