What is the purpose of using (cacheable=true) annotation in Apex salesforce?

To improve runtime performance, set @AuraEnabled(cacheable=true) to cache the method results on the client. To set cacheable=true, a method must only get data. It can’t mutate data.
Marking a method as storable (cacheable) improves your component’s performance by quickly showing cached data from client-side storage without waiting for a server trip. If the cached data is stale, the framework retrieves the latest data from the server. Caching is especially beneficial for users on high latency, slow, or unreliable connections such as 3G networks.