Let me explain the permission hierarchy in Salesforce when it comes to field-level security (FLS):

When both Profile and Permission Set have different levels of field access:
1. The most permissive setting wins
2. Permissions are additive, not restrictive

So in your scenario:
- If you give READ access in the Profile
- But NO access in the Permission Set
- The user will still have READ access to the field

This is because:
- Permission Sets are designed to grant additional access, not restrict it
- They can't be used to revoke permissions that are already granted at the Profile level
- The user will retain the READ access from their base Profile, regardless of the Permission Set settings

To completely restrict access to the field:
- You would need to remove access at both Profile AND Permission Set levels
- Or remove access at the Profile level, since that's the base level of access

Best Practice:
- Keep minimal permissions in the base Profile
- Use Permission Sets to grant additional access when needed
- Don't rely on Permission Sets to restrict access that's already granted in the Profile