I've been asked to try to clarify the different product components within the EHSM space with especially an overview of "overlap" of Component Extension solution and EHS classic. The rapid innovation over the last 5 years has made this a moving target and some different approaches have been taken, for example with respect to the old Industrial Hygiene and Safety application versus product safety topics such as Global Label Management and different again for areas like EHS Regulatory Documentation or Product Stewardship Network.
I suggest that to stay current, consultants should start here and please note that this is a product component view, and is not a 1:1 match to license requirements:
This takes you to all of the official documentation for the
component extension for SAP EHS Management.
In particular, consultants should follow the link to the Application Help (SAP Library) and study what is there.
Then, going back to the main page, if you look at the left panel menu, you'll also see
Apps for SAP EHS Management
SAP Environmental Compliance
SAP Product and REACH Compliance
SAP EHS as part of SAP ERP
SAP EHS Regulatory Content
SAP Product Stewardship Network
SAP EHS Regulatory Documentation OnDemand
Looking just at SAP EHS as part of SAP ERP, the component extension for SAP EHS Management as of the 5.01 release has essentially replaced the following older applications: Industrial Hygiene and Safety, Hazardous Substance Management, and part of Occupational Health (all but the actual medical appointments and medical record-keeping.) The component extension has significantly more functionality in the "people health and safety" areas and is a more collaborative solution rather than "system of record" type transactional system. For new customers, the choice is clear to go with the component extension. For customers with heavy implementation of "classic", they need to carefully consider when is the best time for them to upgrade.
In contrast, for now at least, the product safety applications such as Dangerous Goods and Global Label Management are still in the SAP EHS as part of SAP ERP.
Looking at the product compliance functionality, the component extension for SAP EHS Management is (for now at least) mostly focused on the requirements of discrete industries rather than process industries. It likely replaces the older SAP Product and REACH Compliance, but customer specifics may differ.
The 6.0 release (June 15, 2015) introduced the successor to SAP Environmental Compliance (which is in the JAVA stack) with ABAP Webdynpro in the EHSM component extension. Customers who have already implemented Environmental Compliance do not need to rush to switch over, but can do so sometime in the future when it makes sense for them.
The last three items on the list above are completely different, being content delivery and cloud solutions.
Again, this is a moving target. The development teams are often put in the position of trying to predict the future and are doing their best to leverage new technologies. In December of 2010, when the component extension 1.0 for SAP EHS Management was released to customers, HANA, cloud, and Fiori did not even exist. Who knows what will exist in another few years?