Pro: you know, holding in your farts strengthens your sphincter. this, unbeknown to some, assists in the propelling of sperm from the penis. thus, holding in your farts can actually increase the strength of your ejaculations. good reason to keep 'em in.
Con: spontaneous combustion (for all the south park fans) :1orglaugh
PS: one of the two is real. i'll leave it up to you to decide which.