Legitimate conferences provide an opportunity for knowledge exchange between people from similar fields or different fields with similar interests. They allow researchers to get feedback on work in progress, network and connect with people with whom they might collaborate, seek advice, share data, etc. Conferences also present the opportunity to stay up-to-date on research trends in a particular field or area of interest. They typically come with presentation and sometimes publication opportunities. As a bonus, they may take place in an interesting location. Typically, there is a registration fee to offset the cost of venue, catering, logistical support, etc.
Predatory or scam conferences charge a fee that allows the organizers to realize a substantial profit. They often take place in an appealing travel destination and may promise publication (which is inconsistent with rigorous peer review). Such conferences are not well organized around a theme or field to facilitate productive interactions and lack the benefits described above.
