Erik Darling has some thoughts:
First, I’m not suggesting that anyone should be using the default value for Cost Threshold For Parallelism. It’s old and moldy and not a good fit for most workloads functioning on modern hardware.
My apologies to Azure SQLDB users who can’t change this setting and leave it up to Microsoft to maybe manage it for them based on ???
Some people out there really like fiddling with settings in a usually ill-informed reaction to Some Script They Found On The Internet, without reading the fine print.
Erik’s thoughts are reasonable overall. My recommendation is to use Michael J. Swart’s technique for tuning cost threshold for parallelism as a starting point, as it gives you a basis for what the net effect of your changes are.