Through conversation with the defendant I am able to establish their abilities without a formal, structured approach and in real time. For a number of people being asked to point to a picture from a choice of four doe not reveal their ability to process language in the real world. For example they are not also trying to interpret body language, facial expression and tone of voice at the same time as trying to interpret the spoken message and compete with other distractions. Conversation also allows rapport to be built. This is of vital importance given the length of time you may be working with them in close proximity.
Some people need the formal assessment as a means of warming them up to be able to engage in the conversation element as they find talking to strangers difficult, for example. It is also possible to use it less formally than the instructions may suggest to enable you to gain the target information about the person's communication.
There is no one size fits all and each defendant needs a tailored approach to meet their personality and communication needs.
Some of the defendants I have assessed, I did not feel would benefit from the services of an intermediary either because they have adequate language skills or because their communication needs are such that facilitation would not be sufficient to enable the to actively communicate. Some defendants require the services of an intermediary throughout the trial process whereas some may only need support when giving evidence (for example due to a speech difficulty).