There is no 'well‐known trademark registry' as such, but once an administrative or judicial decision has been made, stating that the trademark is well‐known and ruling in favour of its owner, a record is kept and the owner may use such decision(s) in future cases in order to enjoy additional advantages.
It will also be easier to prevent the malicious registration and use of the trademark by others, even on non‐similar goods or services.
The well‐known status may also be used and an additional argument to prevent the use or registration of trademarks that, in normal circumstances (a 'standard' trademark), might not be considered as similar.
People's Courts are likely to grant higher damages, if your TM is considered 'well‐known'.
It is easier to prevent the registration of the trademark as an enterprise name (whereas if the trademark is not recognised as "well‐known", it is necessary to prove that the mark is used prominently in the enterprise name.
It is easier to prevent the registration of the mark as a domain name (whereas for a "normal" mark it is necessary to prove that actual transactions under the disputed domain name have been conducted).