Using the correct format for play scripts is essential, if not initially, then certainly by the time you’re finishing the draft you show people. “Why should I obsess on format?” you ask. “Isn’t the content of my play more important than how it looks?” In theory, yes, but in the real world, not necessarily.
Here's a comparison that will show you what I mean. Would you go to job interview at, for example, a real estate office wearing jeans and a tee shirt? Probably not. Why? Because you want to make a good first impression; you most likely won’t get a second shot. More importantly, you want to look like you fit in. Like you’re part of the environment you hope to enter. If you want to express individuality, the way to do that is in the work and not in inappropriate dress that will most certainly lead the interviewer to conclude that you don’t get it and you’re not to be taken seriously.
Similarly, when you begin showing your play to people who are in a position to make it happen, you want these folks to think you're a pro, not the opposite. If your script doesn’t look like scripts producers, directors, etc., are accustomed to seeing, they very well might conclude that you don’t get it and you’re not to be taken seriously. Why shoot yourself in the foot?
Believe it or not, theatre literary managers and other script readers – because they receive hundreds, maybe thousands, of scripts to read – look for reasons not to read scripts. If a glance at your first page seems to indicate you’re an amateur or clueless in your presentation of your material, your script might hit the circular file before a word is read. Is that fair? Of course not. Does it happen? Too often. Take the time to put your wonderful story and dialogue into the accepted professional format, and you’ll have a better chance at serious consideration.
Take a look at the script sample I put together. Look at both pages. The sample isn't everything you need to know about formatting, but it's a good place to start.
Play Script Formatting Sample