Volley fire is normally the superior method, but as you said one of the reasons was drilling. The British, French, and Prussians (more so the British and French.) were the most well drilled out of all of the army's in Europe. The British infantry in the late 18th century to early 19th century and beyond were top notch. They were able to easily pull off 3 volleys a minute sometimes 4 which was faster than any other infantry at the time (besides perhaps the old guard.) From the British perspective it was normally beneficial to use volley fire because of their quick reload time, and accurate fire. The fire by ranks tactic was also employed as it allowed for more firepower with multiple lines firing volleys at once. It required excellent drilling though, something the British were known for. It was used against the imperial guard at Waterloo to great effect breaking them very quickly since they had taken horrendous casualties from musket fire, and cannon fire. As for the French, before the late 18th century they did have the superior army, but their men were not as well trained. It was only until the Napoleonic wars that some guard regiments were on par. The Prussians were known for their discipline, and had one of the strongest army's in Europe and they were constantly at war over their borders. They were not quite as skilled as the British though. Some officers and commanders even in Britain had the mentality that fire at will was superior. Though it in theory kills more men the shock to morale created by volley fire is often times more beneficial as the enemy line is more likely to break. Ripple fire is an interesting one as the men fire one by one starting from the officer's side. Again this would not be as beneficial as volley fire, but volley fire can also be a huge waste of ammo. For instance, if you had lets say 1000 men in a line, and you saw about 50 enemy's volley fire would be a huge waste of ammo as 1000 muskets would not at the right range be needed to kill all 50. So fire at will, or ripple fire would instead be used and to avoid wasting ammo, the officer would order them to cease fire once all of the men died. Another probable option would be to charge, but you would end up losing some men as they are charging so it is not always the best tactic though historically bayonet charges are shown to be effective when used properly. Even recently in Afghanistan UK troops were under fire from some Taliban terrorists. The British had little to no ammo so they fixed bayonets and charged using some bushes as concealment. The Taliban instantly broke and the UK troops captured or killed many of them. And amazingly the UK troops took no casualties on the charge which goes to show that they can be effective in some situations. To answer your question, ripple fire and fire at will were used to conserve ammo when volley fire would just be a huge waste of ammo, the men were not drilled well enough, or if the officer believed that fire at will or ripple fire was superior.

In contemporary drill books, battalions were instructed to fire by half companies going along the line to ensure that the battalion was constantly firing. In the heat, shock and confusion of battle, this would inevitably degrade very quickly into soldiers firing individually, usually after only a few volleys. As seen with Maitland's Guards Brigade at the Battle of Waterloo, this could result in two lines of infantry indecisively firing at each other for ages, with casualties steadily mounting (the Guards Brigade and the regiment of the Imperial Guard it faced at Waterloo both staggered away from their dual with 45% losses). Even before this it was recognised that this was hardly an ideal state of affairs: the traditional view of the Peninsular War is of stolid British Redcoats dutifully firing their three rounds a minute into the approaching French column and slowly cutting it to pieces. In reality, the British Army had realised from the experience of North America that the best way to minimise their own losses and win infantry engagements decisively was a massive explosion of fire at close range caused by the entire battalion firing at once, followed by a bayonet charge. This was the genesis of Wellington's famous "reverse slope defence", positioning his battalions behind the crest of a hill to catch French columns as they came over, giving them no time to move from column into line. By the Napoleonic Wars, nearly everyone disdained line-vs-line engagements, with the British adopting the reverse slope defence, the French large amounts of skirmishers, artillery, and the ordre mixte, and the Prussians, Russians and Austrians massed column attacks after they adopted Napoleon's tactics.

Sources:

Paul K. Davis, Masters of the Battlefield

Philip Haythornthwaite, British Napoleonic Infantry Tactics, 1792-1815

Paddy Griffith, French Napoleonic Infantry Tactics, 1792-1815

Peter Hofschröer, Prussian Napoleonic Tactics, 1792-1815