We do randori at the end of a lesson to relax again . After training people's minds are busy with all the stuff they did in the past two hours so it's time to listen to the body's center again. To do that, we have at least two attackers,who can do any attack, to keep nage busy and from thinking and planning. For advanced people nage has to keep his/her eyes closed to rely totally on his/her feelings of where the energy and the flow goes.
Randori is very helpful to learn to trust your body feelings and to become more sensitive to energy flows and how to use them. At our dojo it's introduced at a very early stage (veeery slow at first) and it's amazing to see that beginners come up with all kinds of techniques they were never taught before just by discovering basic energetic and biomechanic principles during randori.