Trackbacks… what do they do?

I’m sorry for the dumb question but what exactly are those trackback links for? I mean… do they really do anything worthwhile? I just have a small personal site wiht my journal… do I NEED them? Is it possible to remove them? After activating that wp-hashcash plugin, now I get trackback spam. So can I remove it all together? Will this affect anything else in my blog?

Thanks.