Your servers have many-core CPUs, right? And you want SQL to utilize those cores to the best of its ability, distributing the many users’ workloads fairly amongst them, yes? Damn right, you paid $3k or more per core in freaking licensing costs! “OK”, says SQL Server, “I’ll use all available CPUs for any query with a ‘cost’ over ‘5’“. (To give context here, in case you’re not aware, ‘5’ is a LOW number; most OLTP workload queries are in the double to triple digits). “But wait!”, you protest, “I have more than 1 user, obviously, and I don’t want their horrible queries bringing all CPUs to their knees and forcing the 50 other user queries to wait their turn!”
Nate has a few recommendations here, as well as a picture of kittens.