"Online conversions" generally refers to the process of converting a visitor from some lesser-valued status to a higher-valued one. Unsubscribed visitor to subscribed visitor. Lurker to commenter. Commenter to contributor. Contributor to customer, etc.

Closely associated is the concept of a "conversion funnel", which measures the fall-off in participation as additional hurdles are imposed: registration, check-in, passwords, browser compatibility, extensions, screen resolution, etc., etc. The results can sometimes be counterintuitive.

For a sense of just how precipitous that fall-off can be, from an example I've got some strong familiarity with, there's this image showing total Google+ registered profiles, the number which were ever active, within the past year, and excluding YouTube activity (which was being included in totals). The net result was about an 0.3% active public participation rate.

https://d324imu86q1bqn.cloudfront.net/uploads/asset/attachme...

Study:

https://ello.co/dredmorbius/post/naya9wqdemiovuvwvoyquq

(My work.)

https://en.m.wikipedia.org/wiki/Conversion_marketing

https://en.m.wikipedia.org/wiki/Conversion_funnel

Lurking encourages user participation in the long run. Sure, a few people will be early adopters and begin contributing with enthusiasm, but a larger chunk of users prefer to consume content passively before making the decision that contributing is worth it for them.

Turning away your potential audience with an immediate demand to register is a great way to make sure your content isn't read.