For which of the following would similar triangles and trigonometry be useful for measuring?
the length of a table.
the width of a wide river.
the length of a car.
the width of the classroom.

To measure the length of a table, the length of a car, or the width of
the classroom, you can walk from one end to the other, and you can
stretch a string or a tape measure the whole distance.

But if you need to measure the width of a river, there's no way to walk
a straight line between the ends of the measurement, and it's almost
impossible to use a ruler or a tape measure.  You have to find another,
more clever way to measure it.

A little bit of trigonometry makes the job easy.  I'll have to admit, though,
I don't immediately see where similar triangles would have to be involved.