Where a couple thinks they agree on all issues, it may seem logical to save money and use one attorney to "handle paperwork". This almost uniformly is a very bad idea. Lawyers recognize the possibility of conflict of interest, in which it is impossible to represent both sides fairly. Most lawyers won't even entertain the idea of doing this.
Using separate lawyers does not have to lead to creating conflict where none existed; it may be invaluable, however, in making it clear that parties have not considered every potential issue, and have disregarded something that may come back to haunt them later.