I have discovered, that symbol fill in PDF converting into pattern and vectorial fills into lines. That means using symbol fills can reduce size of PDF, especially when there are big areas are covered - for example for landscape plans. In DWG opposite - vectorial fills remains as pattern in AutoCAD and symbol fills turning into lines.
By this reason I deleted almost all vectorial fills and replaced them with symbol. To fix problem with large DWG files because of vectorial fill I set in DWG translator fills/hatch conversion table - when all fills are replaced by native AutoCAD hatches.
Also, when I replaced vectorial fills into symbol I matched standard fills number (by using Attribute manager).
As well I introduced short codes for fills like STR for structure, ROOF for roofs etc. - just to easier to find needed fill. You can review my template that I published on this forum - how I organised everything.