Well, it was clearly an important idea for Gygax.It's hard to say what he did in his own games, but he must have realized pretty fast that having the DM rate each player's roleplaying in order to set each PC's training costs was an idea born in the depths of dumbness.
From his PHB, p 106:
clerics' major aims are to use their spell abilities to aid during any given encounter, fighters aim to engage in combat, magic-users aim to cast spells, thieves aim to make gain by stealth, and monks aim to use their unusual talents to come to successful ends. If characters gain treasure by pursuit of their major aims, then they are generally entitled to a full share of earned experience points awarded by the DM.
This discussion of the "major aims" of character classes is more-or-less a summary of the following on p 18:
The approach you wish to take to the game, how you believe you can most successfully meet the challenges which it poses, and which role you desire to play are dictated by character class (or multi-class). Clerics principally function as supportive, although they have some offensive spell power and are able to use armor and weapons effectively. Druids are a sub-class of cleric who operate much as do other clerics, but they are less able in combat and more effective in wilderness situations. Fighters generally seek to engage in hand-to-hand combat, for they have more hit points and better weaponry in general than do other classes. Paladins are fighters who are lawful good (see ALIGNMENT). At higher levels they gain limited clerical powers as well. Rangers are another sub-class of fighter. They are quite powerful in combat, and at upper levels gain druidic and magic spell usage of a limited sort. Magic-users cannot expect to do well in hand-to-hand combat, but they have a great number of magic spells of offensive, defensive, and informational nature. They use magic almost exclusively to solve problems posed by the game. Illusionists are a sub-class of magic-user, and they are different primarily because of the kinds of spells they use. Thieves use cunning, nimbleness, and stealth. Assassins, a sub-class of thief, are quiet killers of evil nature. Monks are aesthetic disciples of bodily training and combat with bare hands.
In his DMG the connection to a "full share of earned experience points" has been replaced by the training rules, but the concept of "major aims" remains the same. From p 86:
Consider the natural functions of each class of character. Consider also the professed alignment of each character. Briefly assess the performance of each character after an adventure. Did he or she perform basically in the character of his or her class? Were his or her actions in keeping with his or her professed alignment? Mentally classify the overall performance as:
Clerics who refuse to help and heal or do not remain faithful to their deity, fighters who hang bock from combat or attempt to steal, or fail to boldly lead, magic-users who seek to engage in melee or ignore magic items they could employ in crucial situations, thieves who boldly engage in frontal attacks or refrain from acquisition of an extra bit of treasure when the opportunity presents itself, "cautious" characters who do not pull their own weight - these are all clear examples of a POOR rating.
E - Excellent, few deviations from norm = 1
S- Superior, deviations minimal but noted =2
F - Fair performance, more norm than deviations =3
P- Poor showing with aberrant behavior =4
S- Superior, deviations minimal but noted =2
F - Fair performance, more norm than deviations =3
P- Poor showing with aberrant behavior =4
Clerics who refuse to help and heal or do not remain faithful to their deity, fighters who hang bock from combat or attempt to steal, or fail to boldly lead, magic-users who seek to engage in melee or ignore magic items they could employ in crucial situations, thieves who boldly engage in frontal attacks or refrain from acquisition of an extra bit of treasure when the opportunity presents itself, "cautious" characters who do not pull their own weight - these are all clear examples of a POOR rating.
These examples of "POOR" play of a character follow completely naturally from the PHB's descriptions of the various classes' major aims and functions. And it's clear that these "natural functions" or "major aims" of each character class were closely associated, by Gygax, with character progression. Poor play in relation to these functions/aims (and also in relation to alignment, in the DMG formulation of the idea) is meant to be a burden on the rate of PC progression.