In that case I really want to remove as much code as possible from this method. using if (DEBUG) is guaranteed to remove the line at compile time when the exact behavior of removing the empty method and evaluation of its parameters (string concat ...) is unclear.
Profiling is already not giving that much information so I want to avoid any possible noise.
From the readability standpoint I think that being consistent and systematically starting debug statements with if (DEBUG) is actually a good thing.