This is always an interesting question, and people will have many different answers. 
Some people are only interested in very practical matters, like controlling when lights come on.
Others get into home automation as a hobby and do all kinds of fun and impressive things that you wouldn’t do without home automation. Like having a smart speaker announce when a particular person has come home even if that person lives by themselves! 
There have been a number of threads in the past discussing this issue. Because the Samsung SmartThings ™ platform has gone through so many changes over the years, the specific methods for accomplishing these automations may be different today, but the goals will be the same, so you should still find it interesting. Just do check the dates on the posts: anything which is more than one year old probably has a different set of devices and rules today than it did when it was written.
(In particular, projects which were done with “routines,“ “core,“ or “rule machine,“ would today be done with “scenes,“ “automations,“ “webcore,“ or “the new rules API.“)
Here’s one of the popular intro threads. (The topic title is a clickable link.)
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And some more from a practical perspective:
FAQ Routine, routines: How do you use them? (SmartThings Classic)
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What are your practical use cases for automation, no "fun" things?
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What are you automating? (UK hub)
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Use cases for color smart bulbs?
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And here’s my own project report on the topic:
Adding Home Automation in Phases: my limited investment strategy