Casting
It can sometimes be difficult to get performers to appear in your films, which makes it tempting to use any willing performer.
However, this can have a negative impact on your film.
If someone is inexperienced at acting or is uncomfortable in front of the camera they will probably not deliver a particularly convincing performance.
If someone looks wrong for a part, audiences may not accept them in the role.
If you're making a film about a tough cop tracking down a hardened criminal, your film might seem silly to audiences if those roles are not played by suitable looking adults.
Sometimes however, films can make use of unusal casting to great effect, like in Bugsy Malone (1976), when all of the main roles were played by children under 17.
Just as it is a good idea to think about the locations you have access to before writing your script, consider who you can rely on to act in the film.