I am going to address this issue from the production side. What happens when you don't show up?
Let's start at the audition:
When you are late or don't show up to an audition, this immediately makes us ask the question.... if this actor was hired, would they be late or not show up to their shoot day? Is their excuse a valid emergency, or just something created on the fly to make the actor feel better about the no show? Do you get a second chance? Sometimes - if we don't find who we are looking for in the first round auditions, we may give you another opportunity to come in. If you miss this second time, don't count on a third.
Next let's talk about other pre-production meetings such as read-throughs, costume fittings, or other things that you need to show up prior to your shoot day. Unless it's a "just show up anytime between such and such hours" type of deal, you have a scheduled appointment time. Whoever you are meeting with has set aside time just for you. You should respect this person's time, as well as any other actors who are coming in after you for appointments and not be late, or call at last minute to rearrange your time.
What about being late on a set day. This covers both actors and extras. Yes, I have had several times that the actor shows up to set late, unprepared, and expects production to just wait on them to get their act together. This is not only highly unprofessional, but you are costing the production company money. This does not reflect well on you and could jeopardize future opportunities (especially bigger, more significant roles). You should always come to set early, and prepared with lines memorized, and any requested costumes in tow.
As far as EXTRAS. Yes, there is a lot of "hurry up and wait" while you are there, but if we tell you that Call time is 10am, you should be there by 9:45am checking in, ready to go. Hair done, makeup done, and appropriate wardrobe in tow.
On extra days, we invariably seem to have someone who is late, cancels at the last minute or just basically doesn't show up. When we are asked to provide specific numbers, especially small days, this is highly important, and will definitely impact your future work, especially audition opportunities. Being an extra is your first step, your "test" of sorts. Can we count on you? Are you a person of your word? If not, then why would we risk calling you in for a role of more significance than an extra?
What about other seemingly minor appointments? Headshot appointments for one. You can expect to be billed at least half or in full for your session even when you don't show up for a photography session. Getting a headshot is a key element of your Actors Tool Kit, and if you can't be professional and take care of business, how do you expect to be taken seriously? Photographers that are recommended do let us know the complications that occur with each headshot session.
You show me that you respect my time, are on time, reliable, and someone that I can count on to show up, then you will see yourself getting booked for smaller scenes, and given more opportunities than those who complain, are always late, or who blow off commitments because it becomes inconvenient for them.
You may think "oh well" or "I'm tired" or "It doesn't really matter" but it does matter, it is a reflection of your work ethic, and the movie biz is oftentimes strenuous, stressful, and fast paced... if you aren't someone who can we can count on to be there, be adaptable, flexible, and go with the flow, then we need to replace you with someone who is.
A good motto to adapt: "I will strive to be a person of character, true to my word, and conscious of my commitments. Knowing that the opportunities allowed me can be taken away at a moment's notice."