A lot of users, myself included, enjoy golfing in practical languages, even though they often stand no chance of winning against the terse and powerful golfing languages.
There are a lot of things that make these languages unique and rewarding to golf in. I like Haskell for its pattern matching, but very much enjoy Python's dynamic typing, and I feel that these are both very fun features to golf with.
What language features make for enjoyable golfing? These features do not have to be features that make a language good at golfing, just features that make golfing in a language fun and reward users for cleverness.
Please include both an example of a language with this feature and an explanation as to why the feature makes golfing in that language interesting. An mini-example answer might look like:
The splat operator is a operator present in Python 3. It allows you to turn a collection like a list or a tuple into the arguments of a function. For example
[*f()] casts the results of
f() to a list.
Splats are fun because they allow you to be more creative with the types you are using. For example if you have a function that takes two arguments, you could calculate them separately and pass them to the function or you could calculate them together returning a tuple that could be splatted into your function . . .