Hi,
Yes, if you put "default edge length" at 50m, your mesh will have a basic resolution of 50m, eventually lower if you specify density objects lower than 50m in some areas.
If you only need 50m resolution in a specific region of your domain, you should define it with density objects instead and put default edge length to an higher value.
To see the resolution of your mesh, you can select the generated mesh and then Tools-->T3 Mesh-->Extract EdgeLengths
Regards,
Laurent