To use or not use

[StageDiz]

I often see that in the design of unsupported walkway or bridge is not used lattice girder (Layher).
They are replaced by a reinforced ledgers and a large number of diagonal brace. Why is this happening.
I have heard that the manufacturer does not give them guarantee or I don't understand something.

 

[DECROMAX]

You can bridge up to 5 bays like this (its in the Layher manual). I have done 4 bays of 2.57m and it seemed good to me. I would rather use beams though.