Rhubarb

[Lamplight]

I have for some time used my old rhubarb leaves as an effective weed suppresant simply by laying them ontop of the weeds and it works rather well.
No doubt that many of you saw the recent Gardeners world special about Allotments.  One lady uses her rhubarb leaves as green manure or for the compost heap.
Is this OK ? I thought it would have a negative affect seeing as it makes quite a good weed control.