elgg architecture design

Hi, all, I quote here from elgg website "Elgg is built on atomic data units called entities. A user is an entity. A blog post is an entity. A group is an entity and so on. There is a base class in the Elgg framework called ElggEntity. All other entity classes extend that class. As an example, the ElggUser class extends the ElggEntity class to provide user functionality.".

I learnt a bit of object-oriented programming, and i understand the use of inheritance and the advantages of using it. however, looking at the elgg database design, it is also designed based on this kind of idea. In comparison with creating a table for individual entity, is elgg method the better way? and more importantly, performance wise, is elgg method more efficient? I would think that since the entity table contains all sorts of entities, such as blog, user and so on, it would grow really big really quickly, which makes searching and editing of a particular record much harder, isn't it?

looking forward to everyone's opinion.

Thanks in advance.