Drupal site with 400 fields and 75 bundles has quite a lag when a view needs to execute. There is an array_filter() called in the views_entity_field_label() function that is called hundreds of times for each bundle. (once for each field basically.) or maybe twice. It just seems to be getting the list of fields and filtering that list over and over. It's fairly fast, but with so many fields and bundles, it starts to turn into .4+ seconds.
The Taxonomy Manager module uses loadTree() in getChildCount() and vocabularyIsEmpty() methods, which load entire term objects into memory to count them. This causes PHP memory limit errors with large vocabularies (over 200K terms). Performance is significantly impacted even on smaller vocabularies.
When we expose a decent amount of entities (for example 30 nodes) with all their reference fields, then our response can become slow.
Most of the time our normalizes will be doing the same job, for example, the same user entity will be normalized 30 times (if all 30 nodes have the same author).
The same will happen if we have circular references (the entity has a reference on itself).
