Although often the problem is producing many rows in the first place, it is made worse by returning all the unnecessary rows to the client. This is especially true if the client and server are not on the same host.
Here are some ways to reduce the traffic between the client and server.
Consider the following scenario: a full-text search returns 10,000 documents, but only the first 20 are displayed to users. In this case, order the documents by ranking on the server, and return only the top 20 that actually need to be displayed:
SELECT title, ts_rank_cd(body_tsv, query, 20) AS text_rank FROM articles, plainto_tsquery('spicy potatoes') AS query WHERE body_tsv @@ query ORDER BY rank DESC LIMIT 20 ...