At the end of Breaking Bad season 4, Walt destroyed super Meth Lab of Gus. Walt already killed Gus, so what's the necessity of destroying the Meth Lab. It brought more DEA attention and some evidence collected from the Meth lab may leads to arrest of Walt and Jesse. So what is the purpose of destroying the lab?
Earlier on in the episode it was detailed that the DEA were already on to the Laundry place (the scene with Hank discussing why a laundry place would need two 1700 amp power panels, and how a laundry of that size would need less than half of that).
While destroying the lab focused the attention of the DEA, they were already hot on the trail anyway. Furthermore, Gus had just been killed, which would have bought additional heat down on the laundry place. Leaving it in tact would have left more evidence behind than what they actually found and clearly demonstrated the scale of the current operation. I'm not sure that blowing it up would have left much evidence tying Jesse and Walter to the scene though, since the vast majority of their work in the lab was done in protective clothing with gloves on.
Walt knew that Hank already was on Gustavo's tail and that the violent death of the latter would accelerate discovery of the lab by law enforcement. Walt could reasonably expect the lab to be discovered within hours.
Walt had to minimise the amount of information law enforcement will eventually be able to learn from the lab and he didn't have any time at all to destroy the evidence selectively. Remember, there were two bodies to get rid off as well? And he had to destroy the manufacturing capacity anyway even if undiscovered by DEA or police - leaving Gus people high and dry - they still could just have found another cook and kicked the production off again.