Logit function in Logistic Regression
W is just the coefficients that we estimate to determine the contribution of each variable to the model. We attempt to estimate the log odds ratio by multiplying coefficients by the input variables that we have. 

If we didn't have W, by default it would just be the 1 matrix multiplied by X, or each variable output would be assumed to affect the response equally (ignoring the scale differences between predictors).