The 49ers could try to improve a secondary that was torched during the playoffs, but they really don't have a huge need.
San Francisco doesn't need a tight end, but Ertz could completely change the 49ers offense. New England has had lots of success with Rob Gronkowski and Aaron Hernandez, and the same thing can happen with Ertz and Vernon Davis. Ertz was coached by Jim Harbaugh at Stanford, and he has experience in a two tight end set because he played with Levine Toilolo at Stanford.
Ertz would be a great complement to Davis in San Francisco's offense. Davis is a speedy tight end, while Ertz has great hands and weighs 249 pounds. Davis dropped a key pass in Super Bowl 47, and while it wasn't an easy catch, it's one that should have been made. Ertz could be a safety vault for Kaepernick, as Michael Crabtree is also prone to drops.
Kaepernick likes to throw the ball hard, and he throws the ball into tight spaces at times. Ertz can catch these passes, and he could develop good chemistry with Kaepernick. In 2012, Ertz was able to catch 69 passes for 898 yards and six touchdowns with two different quarterbacks at the helm. If Ertz is drafted and he and Kaepernick develop chemistry, San Francisco's offense will be even scarier than it already is.
Because the 49ers don't have big holes and because they also own the 34th pick in the draft, the 49ers will be free to take Ertz with this pick. The safety class is deep, so the 49ers can easily nab a talented safety with the 34th pick. Ertz may not be available then, and he's a guy the 49ers want to get their hands on. Ertz is an underrated player and a perfect fit for the 49ers, and he could be exactly what the 49ers need to take that final step towards a championship.