Case lubrication is almost always necessary.  Some straight wall pistol dies are made of carbide which is hard and smooth enough that case lube is not required.  While this is a very convenient feature and saves time, the process still goes much smoother with lubed cartridge cases.  

There are a variety of effective case lubricants on the market.  The general types are:  paste, pad, and spray.  Each have their place on the bench.  Paste lube is the slowest.  Paste lube is also very effective and a great choice if the reloader is reforming cases or performing a tough full length sizing operation, such as when reloading for a semi-automatic firearm where cases can require significant resizing.  Paste lube is also excellent when just a few cartridge cases need to be lubed.  It is very straightforward to apply, simply transfer the lube to the case with the index finger and thumb.  A little goes a long way, if too much lube is applied, it can build up in the die and cause oil dents, generally on the shoulder of the case. 

Pad lubrication is one of the the best ways to lube a bunch of cases fast.  Pad lube is generally a liquid lubricant that is poured onto a slightly spongy pad, then 4 or 5 cases are laid flat on the pad and rolled to apply lube to the cases.  This method can be used for all types of brass cartridge cases.

Spray type lubricants are very convenient.  They are also very effective.  When lubricating rifle cases, it’s generally best to put the cases in a tray and give them a light spray from all for sides, or to lay the cases flat on a rag with the mouth facing the edge of the bench.  Spray the cases, rotate them 90 degrees and give them a second light spray.  When lubricating bottleneck cases it’s important to get just a bit of lube in the case mouth so that the case can pass easily back over the expander ball that will set the inside diameter of the neck.