No. 1: Get healthy
The biggest benefit of the 49ers clinching the No. 1 seed is that they have the opportunity to rest players these next two weeks to get them healthy in anticipation of the playoffs.
The biggest of these injuries is Christian McCaffrey, who has been dealing with a calf issue that flared up against the Washington Commanders in Week 17. If McCaffrey can rest that calf for two weeks and get as close to 100% as possible before the divisional round, that will be huge as the 49ers will likely lean on him heavily in the playoffs.
The Niners have also dealt with injuries on both their offensive and defensive lines. The biggest of these is Arik Armstead who has missed the last four games. It remains unclear whether he will be able to return at all this season as he deals with a foot and knee injury, but it would be huge to get him back in the postseason.
On the offensive line, Aaron Banks, Spencer Burford, and Trent Williams have all dealt with injuries this season. It would be huge to give Williams, arguably the most valuable player on offense, two weeks off. But all of those guys getting a rest would be massive.
In sum, these two weeks of rest for many of the 49ers' main players in both sides of the ball will be huge to allow them to get as healthy as possible for a postseason run.