Servant Evaluation is a function found within the Demon Institute, unlocked at later levels in the Wilderness, that can apply several powerful passive buffs to your servitors, including % boosts to several stats and even additional equipment slots.
-Servitor Evaluation can be considered like a sort of "grading" or "diploma" system that grants boosts to a Servitor if they have achieved specific levels of strength.
-Servitor Evaluation is fueled by Social Points. Each day, players can get one free draw of 10 Social Points with additional draws available for Diamonds.
-There are 10 possible levels of Servitor Evaluation. Each level requires that a Servitor achieve specific minimum values for their highest Attribute, their lowest Attribute and their total Skills Value.
-Once a Servitor has reached all of the requirements for an Evaluation level you can spend Social Points to instantly grant them that Evaluation level, which also grants the corresponding passive buff. The cost in Social Points increases as you go up in levels and you can't initiate an Evaluation on a servitor that does not meet the requirements, which prevents you from accidentally burning them for no gain.
-You will likely find it very hard to get a Servitor's attributes much past 80 (the requirement for the best Attribute for evaluation level 3) purely with Servant Sacrifice as it is very difficult to find easy-to-acquire fuel Servitors with attributes that high.
-You will likely find it very, VERY hard to get a Servitor's Skills Value much past the requirement for Evaluation level 3 if they are not Gold; without the extra skill slots (particularly passive slots) granted to Gold servitors through their sub-attribute training it would take rather extreme quantities of the difficult-to-get upgrade crystals from other Wilderness areas, as well as "wasting" several Active skill slots with skills you don't actually intend on using, in order to get the Skills value high enough on White or Blue servitors.