There are three important exceptions to this rule.
1) Online (approved) translations of the Bible. If the translation is approved for use in CBS classes, then it doesn't matter whether you read it online or in print. Best choices are NABRE, NRSV Catholic Edition, RSV Catholic Edition, and the New Jerusalem Bible).
2) Online concordances. Online concordances allow you to look up any word in a particular translation and find every verse in the Bible that has that word in its text. Both the NRSV and the RSV are available at www.biblegateway.com. The USCCB has the NABRE online, but its search feature is not easy to use (you need to use the search box for the entire site, so you may get results from anywhere on the site, not just from the Bible). But its feature called "Today's Reading" is very useful for finding the correct liturgical readings not only for today, but for any day of the year.