Should I attend a conference even if I don't have a paper accepted there Attending conferences is considered one of the perks of working in academia, for a variety of very good reasons:


networking, meeting new people
cutting edge research results and new directions
advertise your own research (while networking)
(often) nice venues


In some domains, such as computer science, conferences are (becoming) the main exchange site of top work. In some other domains, conferences are considered entertainment. Next to this quality ambiguity, there are some downsides:


travel costs can weigh on budgets of smaller research groups
conference papers more likely to be dismissed by hiring committees than journal papers


A consequence of the first downside is that many groups only allow researchers to attend conferences if they have accepted talks/papers, which is difficult in top venues. A consequence of the second downside is that some researchers prefer to submit top work to top journals rather than top conferences. 

I do consider the second con relevant to the question, as this is one of the reasons for ending up wanting to attend conferences without having any accepted papers.

Given the ups and downs, I would like to assess the importance of attending top conferences (even without accepted talks/papers) for both individual researchers as well as their research groups. 

My field is machine learning, but answers concerning other fields are more than welcome.
I work in computational condensed matter and have attended both computational (or theoretical) and experimental-oriented conferences. When you submit an abstract for a conference in this field it usually does not imply that you are committing to publish that work in the conference proceedings or that you thereby refrain from publishing that work in a journal. Top conferences (in this field) will encourage and give you the chance of publishing in their proceedings, but will not require it.

What usually happens, is that if you can get the paper published in a reputable research journal you do that, and either 1) choose not to submit a proceedings paper or, the option that I find most interesting, 2) submit related technical work that, while still sound and rigorous, might not get published in a journal but will get accepted as a conference proceedings paper.