Advantages of Precedent:
1. It promotes certainty- because like cases are treated alike, lawyers will be able to predict the outcome of a case and so can advise clients; in fact, the Practice Statement points out that certainty is important.
2. It promotes consistency and therefore, fairness- it is only FAIR that like cases should be treated alike; the same rule should govern everyone.
3. Decisions arise from real life situations, so are more detailed and relevant to real life than statutes.
4. Hayek believes that case law (precedent) develops in line with what society wants, so there should be more of it- the law should develop in response to demand.
5. Flexibility- it responds to a changing society, even more now since the Practice Statement, 1066.
Also, you could say that it is more quick than Acts of Parliament at changing unjust/ out of date laws- for example, R v R made marital rape an offence; if it hadn't, it may still be legal!
You could also mention the developments that have come about from precedent (i've done them in another post, e.g Bland which allowd a limited form o euthanasia, allowing life sustaining equipment to be turned off if patients are in a vegetative state. )
Disadvantages of Precedent:
1. Complexity and volume- there are nearly half a million reported cases; it's difficult for lawyers to find a relevant case; judements are long, and ratio is difficult to identify.
2. (Counter-arguing the 'flexibility claim') - Although precedent does allow some flexibility (depending on the court), the rules of precedent and stare decisis usually mean that a judge may be bound by a precedent even if it is recognised as bad law; Lord Denning spoke out openly against having to follow a House of Lords precedent (in Davis v Johnson, re: the use of Hansard), and said that such rigidity in that case was denying women the protection that Parliament had intended; he thought that the Court of Appeal should be allowed to be more flexbile in terms of following precedent.
3. Therefore, bad law can remain unchanded- its only if someone has money and determination to appeal a case that it'll reach the higher court and have a change of being changed.
4. Retrospective effect:
Changes made to common law apply retrospectively- i.e they can affect events that happened before the case came to court (unlike USA which has prospective overruling)- e.g it is not against the law to do something, until, in your case, judges decide to make it illegal; this is not fair. E.g R v R led to two men who had been convicted of raping thier wives saying to the ECHR that at the time when they did, it was not a crime for a man to rape his wife, it only became so AFTER R v R, so at the time of the offence, they weren't breaking any existing law. (This led to SW v UK)
5. Undemocratic:
Judges aren't democratically elected like Parliament, so it is argued that they should not make law; they also aren't answerable to the people.
6. Against thier constitutional role/ the question of 'is it ever ok for judges to make the law?'
Both of these issues i think i've briefly explained elsewhere, please search the other posts!
Just a useful quote:
The case of DPP v Jones, in which judges changed the law on unlawful assembly, caused Bennion to say 'the judiciary is taking powers to which they are not constitutionally entitled.' (You don't have to remember this, just added it to give some authority.)
Hope that helped, please search up the bits i said (sorry if it was brief, I'm a bit short of time) . I'll try and help if you need anything else (but no promises in case i can't keep them) Good luck!