Not only will this help you gain a clearer understanding of their skills, aims and career direction making it more likely that you'll find them a position they really want, but it will also help you to present them more effectively to your client. If for some reason you can't do an interview with the candidate always be upfront with the client and tell them.
After submitting your candidate's CV to the client you will need to provide the candidate with all the information you can on the client company and the requirements of the job they are going for. They will also need to know if your client is going to have any specific requests for the interview, such as giving a presentation or testing specialist skills.
It is definitely worth getting feedback from the client on the suitability of the candidate CV you've provided. This will help develop your relationship with your client and help you to gain a greater understanding of their needs and the type of candidate they are looking for.