Well, yes, but when you are new to the field, you usually will only know the names of the really big players. Association job boards, and assn boards in general, will help you learn the names of other companies, which of course you can then target directly. Lots of new graduates "don't want to work for" a company not because it has a bad reputation, but because they have never heard of that company. Many times smaller companies are very good places to work, but not household names except for a tiny in-the-know minority, which students, even grad students, usually are not part of unless they have family ties.