Any pro's and con's of whether the definition of plan compensation should/should not include salary reductions pursuant to 125, 401(k), etc....... other than the fact that including will yield a greater contribution and excluding will yield a smaller contribution? Employer maintains a PSP and a welfare benefit plan (health/dental).

if HCEs comp > 200,000 then excluding deferrals will help testing as the HCE comp does not change.
On the negative side, it penalizes the lowly NHCE from deferring as it results in a smaller contribution. sort of like using match to satisfy top heavy. why bother deferring when your co-worker gets something for nothing by not deferring.