It is not recommended to sow a new set of replicas using mongorestore, why?

Question

In docs, I found the following statement:

IMPORTANT Always use file system snapshots to create a copy of an element of an existing replica set. Do not use mongodump and mongorestore to launch a new replica set item.

• what i need to do if my FS does not support snapshots and
• why is this limitation here at all? Previously, you could use the mongodump snapshots you created to add new rs members (edit: if I'm not mistaken).