Various functions which are available as part of Transformer can be performed by various other individual specialized stages.
Lets take example of Constraints which can be achieved by Filter Stage and so is Metadata Conversion by Modify Stage. Copy Stage can take care of copy of field and producing multiple outputs and Column Generator can create new fields. Surrogate Key Stage meant for counters. So Transformer provides them all at one place but for performance should use these highly specialized and faster stages. The reason these stages can perform faster because they do not carry as much overhead. Also it is the ease of use as when you want to use Specialized Stages it is not "Fun". You need to be expert and so is understanding other developer's mind and may be well defined strategy to work with these specialized stages.
The Transformer is hands down the best stage to write any type of transformation code in the entire DataStage product given the right mouse click menu, the red text marking for syntax errors and the grid layout.
The transformer stage is one of the few stages that has a robust reject link for rows that fail transformation. The Modify and Filter stages lack this link so if a piece of data defies logic the job will abort rather then drop a row down a reject link.
Similarly DRS Dynamic Relational Stage and Now a Connector as well is another in the All Rounder Category. DRS Stage and Connector provides all RDBMS connectivity at one place. You don't need to use multiple Plugins or Connectors and instead can use this one and connect to any database. Though with Connectors you get same look across but still it is ease when use "Single Stage" for all database operations. Simple benefit, assume you moved from Oracle to IBM DB2 or from Teradata to IBM Neteeza go to Job, Select Drop Down and move to new Database "So Simple". No need to remove one stage and add another. "But it is recommended to use specialized Connectors or Stages" when you are not having multiple databases in house.