Firstly, manumission may present itself as a sentimental and benevolent gesture. One typical scenario was the freeing in the master's will of a devoted servant after long years of service. This kind of manumission generally was restricted to slaves who had some degree of intimacy with their masters, such as those serving as personal attendants, household servants, secretaries and the like. In some cases, master and slave had had a long-term sexual relationship, perhaps with tenderness felt on one or both sides. Some manumitted slaves were the offspring of such sexual encounters. While a trusted bailiff might be manumitted as a gesture of gratitude, for those working as agricultural labourers or in workshops there was little likelihood of being so noticed.
Such feelings of benevolence may have been of value to slave owners themselves as it allowed them to focus on a 'humane component' in the human traffic of slavery. A cynical view of testamentary manumission might also add that the slave was only freed once the master could no longer make use of them. In general it was also much more common for old slaves to be given freedom, that is to say once they have reached the age where they are beginning to be less useful. Legislation under the early Roman empire puts limits on the number of slaves that could be freed in wills (Fufio-Caninian law 2 BC), suggesting a pronounced enthusiasm for the practice.
At the same time freeing slaves could also serve the pragmatic interests of the owner. The prospect of manumission worked as an incentive for slaves to be industrious and compliant, the light at the end of the tunnel. Roman slaves were paid a wage (peculium) with which they could save up to, in effect, buy themselves. Or to put it from the master's point of view, they are providing the money to buy a fresh and probably younger version of themselves. (In this light, the peculium becomes an early example of a "sinking fund".) Manumission contracts found in some abundance at Delphi specify in detail the prerequisites for liberation. For instance, a female slave will be freed once she has produced three children over the age of two. That is to say, the slave is freed after having replaced herself. Any slave could be manumitted for performing a heroic deed, as in one slave was qualified for manumission after saving his masters family from a burning house. Many slaves had to be released in manumission through will, but this rarely worked.
In both Greek and Roman societies ex-slaves required the permission of their former master to marry.