In leukus a full flared relatively large pommel plays a big role. As a large knife it's meant to be used also in chopping tasks, and this type of pommel prevents the knife from sliding out of the hand even when your grip ain't that tight. It also makes it possible to wield the leuku just by holding it from the pommel. This is important with a bit shorter bladed leukus, to give more leverage for chopping.
In areas where leukus are from, the winter and cold period of the year is very long. So quite often you wear gloves, even very thick ones, so obviously a knife with flared full pommell is much easier to unsheath.
I prefer to make leuku blades few millimeters less in width than the handle, so the knife can be sheathed/unsheathed without compressing the sheath mouth.I find that feature more important than the extra weight near the tip given by the blade widening drastically. This is very common with many leukus, but as well it's quite common to see leukus which have a wider blade and you have to press the mouth of the sheath flat when pulling the knife out. If you want more weight at the front, then I rather forge the blade getting bit thicker towards the tip.
Basic barrel shaped puukko is an all-rounder, very common style in Finnish knife culture. Puukkos with some kind of a pommel are common too, but I would say this barrel shape is the most common in historical point of view. Birch bark provides good grip even when wet, which helps not only in use but also when unsheathing the puukko.