Q:

Need to center continuous variables in GAMs?

This is just a quick question, but I remember reading somewhere that continuous variables used in splines for generalized additive models ought to be centered (especially for GAMs rather than just as a general rule of thumb for models).
However, I now can't find that advice anywhere and wonder if I perhaps read something wrong.  
Is it really best practice to center all continuous variables used in GAMs or GAMMs?

A:

There is no requirement to centre variables with GAMs. The basis expansion applied to a variable (or variables in the case of tensor product smooths) is subjected to identifiability constraints, which typically centre the smooth about 0 via a sum to zero constraint, but this happens whether you centre the variable or not.
It can help computationally to centre variables however, as it places the intercept within the range of the covariates rather than extrapolating out to give the expectation of the response when all covariates are equal to 0.

