Construct 2 has two licenses: a personal license and a business license. If you use Construct 2 without any license, it means you're using a free edition.
The free edition has the following limitations:
Buying a license removes these limitations. Also, even though Construct 2 can't be used for commercial purposes, it can still be used in educational or non-profit organizations.
The benefits of procuring a license are as follows:
Buying a personal license gives you complete access to Construct 2's features, without any limitations. The only rule is that once the total revenue that you got from the products you made using Construct 2 exceeds $5000, you must buy a business license. Educational and non-profit organizations can purchase a personal license to remove the limitations of a free edition. If you're a legal business institution, for example an LLC (short for Limited Liability Company), then you must purchase a business license.
A business license is only meant for two kinds of people: individuals who have made more than $5000 from their Construct 2 creations or from a legal business. Non-profit organizations never need a business license.
Note
You can purchase licenses from http://www.scirra.com/store/purchases.