links make you part of a community
Links can be both good and bad.

Good links from your site to other sites and especially from other sites to yours are good. Use Alt tags and indexs to get the most and wrap your text in links.

bad links
Some SEO companies will offer you multiple submisions to sites and will link you to all sorts of sites in what is called link farming. this is not regarded as a good thing by search engines as they do not bring good content to the web. The link farming are generated links that dont really supply any benefit other than getting links to websites.

If you look at the webmaster notes on search engines they will actually advise you not to use these type of SEO agents for when they find these links the site will be penalised.

stick to good links and content for good search engine optimisation(SEO) and make your site search engine friendly