Praise be to Allaah.
Shaykh Muhammad ibn Saalih ibn ‘Uthaymeen (may Allaah have mercy on him) was asked this question, and he replied as follows:
No one doubts that these tapes are one of the means of acquiring knowledge. We do not deny that Allaah has blessed us through these tapes from which we have gained a great deal of knowledge, because they have brought us the words of the scholars no matter where they may be.
Here in our homes, there is a huge distance between us and this scholar, but it is easy for us to hear his words via this tape. This is one of the blessings that Allaah has bestowed upon us. Indeed it is proof both for us and against us, for knowledge has spread widely through these tapes.
With regard to how we may benefit from them:
This depends on the situation of the person himself. Some people may benefit from them whilst driving, others may listen to them whilst eating lunch or dinner, or drinking coffee.
The point is that the way in which benefit is derived from them depends on the individual himself; we cannot lay down any general rules.