There are advantages to wearing a dancebelt under tights. Mostly support for your genitals if you're not dancing. A thong dancebelt eliminates the "panty lines" of underwear or a jockstrap.
If you want your costume to be accurate, know that in medevil times the guys didn't wear anything under their tights, so the lines were clean. Many guys back then wore cod pieces to emphasize their genitals, but that's something we don't do nowadays when we wear these types of costumes. Nowadays when men wear costumes that include tights on stage, the mode is to wear a thong dancebelt.
Most guys today are concerned that people will stare at their crotches when the guys wear tights. A dancebelt can "smooth" out the look so you don't give the audience an anatomy lesson. Some guys have the balls to give an anatomy lesson, but they are a minority.
What would make you comfortable? Go with that. Consider a dancebelt where you wear your equipment "up." Draw the testicles up out of the crotch and make sure the penis points up towards your belly button. With a dancebelt, this provides a uniform look that doesn't draw attention to your equipment. If you point things down, the bulge is much more obvious.
You need to be comfortable on stage. Please know the 90+% of your audience know what's down there, and know that a performance of knights in tights is going to have what you fear. But that's no reason to fear. A performance is a performance, and most people in the audience will understand and go with the story.
balletboy[/i]