Effectiveness is basically the ability to produce an effect. It entails doing the right things. When you are effective, you set the right targets and your aim is to achieve an overall goal.
On the other hand efficiency is defined as doing things in the most economical way. In other words, it is best utilization of resources. It is doing things in the most economical manner.
Efficiency = Input /Output
These two concepts are very important for organizational behavior. An organization has to be effective and efficient in order to be productive.
In Google Tag Manager https://www.owox.com/blog/articles/online-forms-efficiency/ there are several ways to track a form. Tracking is an art and there is not just one best way to do it. The conversion rate is one of the simplest and at the same time most important measures of marketing efficiency. It shows how many users have completed a target action: Made a purchase, signed up for emails, requested a call, etc