With overall expense being a top consideration for most of us, we all want to save money where we can. However, don't be tempted to secure your venue for the minimal time if you're going to have things to set up.
The length of access time needed before your event depends entirely on how many details you have to put together, how much help you have to get it done, and often more importantly, the experience of your set-up crew. Yet, even the best crew still requires ample time and access. (You might be surprised at how long it takes to dress 20+ tables and 100+ chairs.)
So what's the ideal solution? That depends on how much decorating you want to do. Utilizing a high-end venue? Try keeping the details to a minimum and negotiate your pre-event access BEFORE coming to any pricing agreement. This is the time you hold the most bargaining power.
On the other hand, a parks building or even a hotel banquet room will often allow early access for little or no cost. And if you plan for an elegant, formal setting complete with linens, chair covers & sashes, center-pieces, etc, it may be well worth renting for the day prior as well. Just think of it as an investment in your sanity...and knowing details won't be missed because you ran out of time.