Differences leading & non-leading ledger

our understanding is that the leading ledger has become less important since the introduction of "Universal Parallel Accounting".

Could someone explain to us what differences the leading ledger currently still has compared to the non-leading ledger?

What are the advantages of activating a ledger as leading and what are the disadvantages of activating it as non-leading?

And do the SAP best practices recommend to either use local GAAP or IFRS as leading ledger? If so, what are the reasons for the recommendation?