Final answer:
When using the Schema Builder in Salesforce, remember that field level security for custom fields is read-only by default and requires adjustment for proper user access.
Step-by-step explanation:
When using the Schema Builder in Salesforce, one major consideration to keep in mind is that field level security is set to read-only by default for custom fields. This is important because it has implications for how users will be able to interact with these new custom fields across different profiles. It is important to review and adjust the security settings to ensure that users have the appropriate level of access required for their roles.