How are design agenices using Creative Cloud?

You should contact your colleagues at other agencies and ask them what they use.  Their replies will probably vary depending on the customer and project at hand.

Below is a brief breakdown of the top apps and services, in no particular order:

Adobe XD is good for UI/UX prototyping and reviewing by stakeholders prior to building the actual app in Dreamweaver or some other code editor. 

Adobe Fonts has thousands of curated typographic fonts to choose from.

Adobe Stock has thousands of royalty free photos, vector illustrations, templates and videos for you to use in projects.

Adobe Spark is an online service used by marketeers and social media mavens.  Adobe Portfolio and Behance are more online services used to showcase examples of your creative work online.

Acrobat Pro DC is essential for pre-press set-up of high quality printed artwork. Ask your print professional which settings to use.  Acrobat DC is also used for creating interactive forms and other PDF files.

Lightroom & Lightroom Classic -- a digital darkroom and considered a 'must-have' by many digital photographers.

Creative Cloud Libraries.  Save, browse, and share assets (fonts, colors, stock images) from libraries right inside your Creative Cloud apps.

Character Animator is used to animate Photoshop or Illustrator cartoon puppets.

Post back if you have any specific questions.