Dolphins are the only animal that have sex for pleasure

In fact, dolphins are the only species to have sex for fun besides humans and certain types of monkeys.

Generally speaking, animals cannot afford to waste precious energy that is needed for hunting or defending themselves. Animals have competition so they often get injured or even killed in attempting to find a mate.

The mating process is difficult and time-consuming. Most species look at reproduction as a more natural process and not as a leisurely activity.

(Source)