Does having too many content types negatively affect site speed and performance? I building a site that could potentially utilize 20 different content types. The content types are very similar, but may only utilize one or two fields that are unique to that content type, and they would use the same 5 fields with each other. Does having 20 different content types slow the site down? Would it be better to build one content type and display the unique fields on a case by case basis using FAPI or the conditional fields module?
The number of content types does not affect the performance of a Drupal site.

Sharing fields among the content types does affect the performance. This is because of the way CCK stores fields.


If the field is not shared and allows only one entry, it is stored along with other such fields in a table designated for that content type. That way, all such fields can be loaded in a single query.
If the field is shared or allows multiple entries, the field is stored in its own table, making an extra query (or join) per field necessary to load the field.