One only really notices the oil-sump when, for some reason, it's not functiong properly. Perhaps when driving in very uneven terrain, it came into contact with the ground, which is seldom nowadays because the entire underside of the car is paneled, and in off-road vehicles, because of the special underside protection, it almost never occurs. There may also be something wrong with the sealing to the engine block. In the worst case, the mechanic may have botched something up.
The oil-sump is in fact, a pretty unsuitable point to jack up the engine. There should be a suitable fixture which reaches around the oil-sump and is mounted to a fastening flange. If the sump is made of pressed sheet metal (see picture), it can easily be dented, possibly also causing it to contort, making a good seal unlikely. More expensive oil-sumps made of Al-Si alloy can crack, or even break when wrongly handled.
There are also horizontal divisions with a cast upper-part and a sheet metal lower-end. The sealing between the two can be done with a solid gasket(s) or by using a sealing compound. As far as repairs are concerned, a one-piece sump has the advantage for the mechanic that it can be removed, e.g., to replace the seal, mostly without having to take the engine out. Sometimes however, the sump also functions as a stabilizing element between the engine and the gearbox, which makes things even more complicated.
For a long time, the oil-sump in engines on which high demands were made, played an important role in the cooling function. In this case, even without dry-sump-lubrication, the amount of oil could be increased and through a labyrinth, the path of the dripping oil could be increased before it was again taken into circulation. Additional vanes in cast-iron sumps strengthened the cooling effect. It would appear that other oil cooling methods, e.g., through heat exchanging with the coolant, have taken over this task. After all, a larger amount of oil must also be brought up to operating temperature. Heaven help us, if the oil is still cold and the demands on the engine are still made.
The oil sump is also important for the defoaming of the oil.
On the other hand, because of weight reduction, oil-sumps made completely from synthetics or a combination of metal (aluminium) and synthetics have now become more meaningful. The sumps can even be double-walled. With sumps made from synthetics, it's the same as with modern fuel-tanks: One can utilize every square inch of space and possibly even, accomodate additional components (see picture 2). If you're thinking of the oil-filter, basically this is correct, although however, for servicing reasons, it is today mostly mounted up in the engine compartment. Thus also the valve-cover has become a complex component, of course, also made from synthetics. 09/12