First things first. If your chosen simulation requires a sample post, do not skip the sample post. That's a surefire way to be rejected because they have a sample post requirement for a reason. Most will offer prompts and allow for links to writing you've done elsewhere. If you provide links to your writing and it involves other people as well, state who your character is in each piece.
The sample post is how game managers judge your writing ability. Your writing shows your use of grammar and syntax, as well as how well you can use “realism within reason” to adapt to a simulation. The game manager will read your sample and look at your writing style, which shows them a surprising amount of detail about you as a writer.
You might be wondering how we can determine these things from a block of words on a webpage. The thing is, most game managers have been in the role playing and simming business for a long time. LadyLeopard, the wiki-mistress, started role playing online in 2005, but she began her exploration of writing believable stories in the mid-1990s. Azmaria, the webmistress and hostess of many simulations in the Alliance, began her role playing with tabletop games before online role playing became a trend. These are just two examples of the long history most game managers have before they step into the management role. (LadyLeopard and Azmaria co-manage the Hera and are game managers on multiple Alliance simulations.)
So do LadyLeopard and Azmaria. They still provide writing samples when required.
Now, if you're invited to a game based on the merits you've shown elsewhere and the game manager knows you, you might be able to get away with not providing a sample post. However, it's best to provide one anyway because their assistant game managers might be the ones looking at your application, and they might not know you. It's best to just get in the habit of providing a sample, as that's how most simulations are going to decide whether to accept you and whether they'll give you the role you've asked for. That's just part of role playing.