The exact perturbative calculations for the gauge boson fusion processes W/sup +/W/sup /minus// ..-->.. W/sup +/W/sup /minus//, W/sup +/W/sup /minus// ..-->.. Z/sup 0/Z/sup 0/, and W/sup +/W/sup /minus// ..-->.. H/sup 0/H/sup 0/ are compared with the corresponding effective gauge boson calculations. These comparisons enable us to study the several forms of the gauge boson distribution functions and draw some conclusions about their non-leading terms. In addition, it is possible to study effects of various rapidity cuts on the exact and approximate calculations. For rapidity cuts /eta//sub C/ satisfying 1.0 less than or equal to /eta//sub C/ less than or equal to 2.0, the agreement is excellent. Larger rapidity cuts reveal factor of 2--3 disagreements when the invariant mass of the final state is large compared to the Higgs mass. In all cases, the agreement near the Higgs peak is good. The discrepancies are discussed in terms of the extra diagrams which occur in the exact calculations and the t-channel singularities which are present in the effective gauge boson calculations.