Well. To start with, link-only answers blatantly violate guidance given in How to Answer instructions:
###Provide context for links
Provide context for links
A link to a potential solution is always welcome, but please add context around the link so your fellow users will have some idea what it is and why it’s there. Always quote the most relevant part of an important link, in case the target site is unreachable or goes permanently offline.
By doing so, link-only answers set a bad example for Stack Exchange users, similar to how it happens with broken-windows questions: "why can't I answer link-to-X when link-to-Y answer exists".
Community benefits of removing (more precisely, converting to comments) link-only answers are eloquently presented here:
If a link-only answer is accepted, it is especially important to delete it (converting to a comment if the link isn't broken yet)... When a question has an accepted answer, it looks like it has a definitive answer, and there is not much point in looking for a better one. People who are looking to improve the site by providing better answers tend to consider questions with accepted answers as very low-priority. If a question has an accepted answer which consists solely of a link, this sends the wrong message, especially after the link breaks. Sure, the accepted answer might have helped the asker, but it's not going to help future visitors, and the community should not be penalized for that answerer or asker's failing.
Given above, it is not surprising that official FAQ -> Why are some questions or answers removed? specifically targets link-only answers:
Answers that do not fundamentally answer the question may be removed. This includes answers that are … barely more than a link to an external site
PS. Out of curiosity, I made a link-only version of above answer, wiping out the relevant quotes that were taken from links. Take a look and make up your mind:
To start with, link-only answers blatantly violate guidance given in How to Answer instructions. By doing so, link-only answers set a bad example for Stack Exchange users, similar to how it happens with broken-windows questions. Benefits of removing (more precisely, converting to comments) link-only answers are eloquently presented here. Given above, it is not surprising that official FAQ -> Why are some questions or answers removed? specifically targets link-only answers.
What an impressive saving of a precious screen space. Or not so precious.