When writing I find it is always best to keep a few things in mind: the mood you want to achieve on a given page, and the intended audience.
Both come into play when dealing with romantic subplots. Another factor here is your actual story. Does a romantic subplot move the story along/help facilitate the characters' journeys?
For instance, both comics I'm actively working on right now have romantic subplots. The first of the two is a slice of life/superhero/silly/lighthearted piece. To be honest, the romance doesn't really move the story along but it's a nice distraction from our hero's everyday life (she creates chaos wherever she goes) & her villain fighting. The romance kind of ticks the comedic relief box, if you will.
My other series I am scripting currently is definitely an action/adventure that touches on some of life's darker elements. There are a few romantic subplots, and while at times these moments offer comedic relief, they also help to move the plot along. One reason for this is that I've got a main cast of 5 twenty-somethings who are finding themselves in treacherous situations pretty consistently (fighting 'demons'). Naturally, if you're spending enough time around a group of people at that age, someone is going to develop feelings at some point.
Secondly, as I mentioned, the characters' actually grow/develop through their romantic relationships with others. For instance, in a scene between two characters meant to be shipped together, Character A in trying to build some rapport/trust with Character B, opens up to Character B and reveals the reason he is so obsessive about how well their team performs hunting demons is because he intends to find the demon responsible for killing a family member and they won't be assigned to more difficult cases if they cannot successfully accomplish the ones they've already been assigned. This makes Character B start to put more effort into their work, whereas before Character B blew their training off and didn't care.