The Supreme Court ruled in Rodriguez v. United States (2015) that K9s cannot be used in traffic stops (without cause) if it delays the driver. Period. Previously, the law of the land was that the driver couldn't be delayed too much. But it wasn't clear how much was too much. Waiting for a K9 unit was too much. But if the dog was already there, then it was considered OK. No longer.
Both as a constitutional issue and a strike against the war on the drugs, I think this decision is eminently reasonable. I'm never liked fishing for drugs. And telling otherwise innocent people to wait while dogs sniff around is like a police state. (And besides, we should be skeptical of probably cause based on a dog. Have you ever seen a dog put on the stand?)
K9s can be really useful to police. To search large buildings, for instance. (Another break-in at the Monument Street Market?) And the threat of calling in the dogs is useful in getting some idiot to come out of his hole he crawled into.
Post Rodriguez, to search with a dog without cause means you'd have to have another officer doing the traffic stop part while the K9 does his business at the same time. This won't change policing too much, since there aren't too many K9 units anyway. But it does make me wonder what those K9 units are going to do when they're not needed for real police work. I guess they can still give traffic tickets. But it makes the dog kind of superfluous.
I also think it's important to point out that this will (slightly) increase officer safety. The police academy is filled with videos of cops getting attacked and killed when they start asking to search a vehicle for drugs. Now one could argue that finding and arresting criminals is part of the job, but if your primary concern is officer safety, the safest thing to do in a traffic stop is give a ticket and let the car drive away.