In the simple linear regression model
Y_(i)=\beta _(0)+\beta _(1)x_(i)+\xi _(i)
the intercept is typically small and unimportant.
\beta _(0)+\beta _(1)x_(i)
represents the population regression function. the absolute value of the slope is typically between 0 and 1.
\beta _(0)+\beta _(1)x_(i)
represents the sample regression function.