As per STAAD help file, about parameter EUDL, it says "Equivalent u.d.l on span of the beam. This load value must be the unfactored load on span. During design the load value is multiplied by a factor 1.2. If no u.d.l is defined factored shear force due to gravity load on span will be taken as zero. No elastic or plastic moment will be calculated. Shear design will be performed based on analysis result.(Refer note)". This implies that if EUDL (or GLD) is not specified, the result is unlikely to be correct. Hence, it is recommended to use the GLD parameter (referring to a DL+LL combination, immaterial of whether it is factored or unfactored) as it is a simpler way to define the Equivalent udl.
Hope that helps
Arunkumar
Hope that helps
Arunkumar