Silent calls are generated from the use of 'automated diallers'. When these are incorrectly set, more numbers are dialled than there are operators available to take the calls. If the purpose of the call was to sell you a product or service, then registering on TPS will reduce these.
However companies use automated diallers for things such as debt collection, market research etc. and TPS will not reduce these. Please see the Guidance Notes which the Information Commissioner's Office have produced - Privacy and Electronic Communications (EC Directive) Regulations 2003 and the Ofcom website
If you want to reduce these types of calls there is a separate service called Silent CallGard. You can register with them by calling 0844 3722325.