What is the difference between administrative convenience and specialisation?
Administrative convenience = related to general organisation (a court that doesn't specialise in complex cases shouldn't have to deal with them, because that'll just mean more delays, since the court would need to give in more effort and find resources to solve that case) So that's why higher courts where judges have greater legal expertise and knowledge can hear the complicated cases, so that simpler cases can be solved quickly in Magistrates' Court.
Specialisation - related to competency (right to have case heard in a competent court / tribunal) --> Because only the specific cases are heard in each court (e.g. Magistrates can only hear summary, indictable heard summarily), so it can develop expertise in this area and be on top of things for these types of crimes. The court knows the pre-trial, trial procedures very well, thereby it can give the best possible (as in fair and equal) sentence that the accused deserves. Same applies for higher courts. They can develop comprehensive resources on the complex or lengthy cases that they here, so that means they have more experience in dealing with those types of cases
Hope I make sense