I'd recommend not to do so. That is an easy and cheap way of writing a story. Let me explain :
Some people will include characters that are only there in order to help their main character. So for example, their main character is in jail and obviously, the plot can't go on until he's out of there. Instead of finding a clever and interesting way of getting him out, they decide to include a character that saves the day. Later on in the story, when the character is in trouble again, the same other character comes and save the day, again.
To me, that way of evolving a story is ridiculous and cheap. You have more imagination than you think, so use it.