When it comes to outbound links, there is a lot of controversy as to whether they are useful, have no effect, or create a negative effect when it comes to link-juice or page-rank. The truth of the matter is that most of the people that find outbound links to be completely negative, are looking at their search engine optimization as a formula, rather than trying to sincerely build a useful website that the search engines will recognize as such.
Yes you can follow the mathematical formula to the letter, and rank your site high in the search engines, without providing readers with what you have promised that you would, while following the formula, but eventually you will be found out and penalized by the search engines.
It is usually fine to have under 10 outbound links that your site that readers will find useful. In fact it will make you look more sincere in your intentions to build the site in the first place. But having too many links on your site is completely unnecessary, and will do more damage in the end. It will take away from your page rank, and it will place you lower in the search engines. Mathematically the search engine does penalize you for useless links. But if you are providing your readers with good resources through your links, then keep a few there.1)
When you are trying to determine which links to allow, make sure you look completely through the site you are considering linking to. Make sure that the site looks good, and provides great information or resources to your readers. You want to avoid linking to link exchanges, and other spammy looking sites if they are irrelevant to your website subject matter. Linking to these types of sites can cause you to be penalized by the search engines, because the search engines consider these sites to be spam, and gives them a naturally negative score, which in turn drags your score down.
The hard reality for most to accept is that your outbound links will be helping the site you link to, gain better rankings, more than it will help your site. But if you genuinely want to provide a site that is useful to readers, and handle your own link building, content building, and keyword research effectively, you will be rewarded with decent ranking. If you want to be selfish, and not provide your readers with any useful links, then that is your choice. But it is not necessary to completely avoid using outbound links altogether. Just use them in moderation, and make sure they are both relevant and helpful. Your users will be thankful, and trust you more for it.