That's a tough question, too many factors. Some laptops get almost close to desktop in CPU department (my MSI Titan GT77 can cool 150W CPU for hours, no problem, but most laptops will cut to 50-70W maximum). For GPU, the laptop version is +/- 1-2 models lower in performance tier than Desktop.
The bigger the laptop, the more it is like desktop, but we're talking the really big 17-18" 3-4KG laptops.
Ultimately though, even super powerful laptop like MSI Titan, will be super loud, like airplane loud when you unlock the full performance for rendering. Almost 60dB. It's really something ;- ).
I only use laptop when I am travelling, I would not use laptop as my only PC. It's still laptop in the end.