In general terms, ADR is likely to be both cheaper and quicker than recourse to the courts.
Alternative dispute resolution procedures are also confidential, which means that they may be particularly useful in resolving disputes on matters which are themselves confidential - for example, because they involve industrial secrets, or commercially-sensitive terms of trade.
Mediation is also a very good way of dealing with disputes where the parties want to emerge with a continuing relationship, partly because the object of the exercise is to create an outcome from which all parties benefit, and partly because the confidential nature of the proceedings means that no-one is seen publicly to 'lose'.
Under the Civil Procedure Rules, judges now generally expect the parties to have considered the use of ADR, before commencing court proceedings.