Well, given the fact that my wife has a much lower sexual appetite than mine, this is a must for my mental well-being!
Writing or reading a hot fantasy story will usually put me in the proper mood!
Sometimes, just placing two pictures next to each other will be enough for me to imagine some nice fantasy tale!
E.g. This sophisticated Parisian woman meeting these strong and healthy Senegalese soldiers in 1918. Hmmm... I'll give her some help, because that's a lot of men for only one woman!