questions regarding setup a new barman server

Hi,
I'm trying to configure a barman server that would manage the backup and
restore in the cluster in our company. I'm trying understand a few things
and I have many questions. I would be happy to get some anwers :

1)I decided to use the streaming option for the backups - for wals and for
full physical backup with pg_basebackup. However, I was asked (according to
documentation) to configure the archive_command. My question is why ? Is
there a reason to use the archive_command and the streaming
(pg_recievewal) option ? Now, If I disable the archive_command and use only
the streaming option, to automate the process of recieving wals I need to
run for each server : barman receive-wal my-pg-server ? Is there a reason
to have both archive_command and streaming option ?

2)When I use the command barman receive-wal ptktl-psgsqldb1 I'm getting the
next output once a wal is switched :
ptktl-psgsqldb1: pg_receivewal: starting log streaming at 1F1/F7000000
(timeline 3)
ptktl-psgsqldb1: pg_receivewal: finished segment at 1F1/F8000000 (timeline
3)

However, I dont see those wals in the incoming directory. Why is that ? Is
it just an alert for a switch or a message that means that that wal was
recieved ?

3)When using the check option I have the next error :
empty incoming directory:
FAILED ('/PostgreSQL/barman//ptktl-psgsqldb1/incoming' must be empty when
archiver=off) but I set streaming_archiver to on. Moreover I dont see any
errors in the errors directory.

4)When I tried to take a full backup via barman backup ptktl-psgsqldb1 it
seems that the backup is stuck :
Starting backup using postgres method for server ptktl-psgsqldb1 in
/PostgreSQL/barman//ptktl-psgsqldb1/base/20180715T114042
Backup start at LSN: 1F1/FB040E28 (00000003000001F1000000FB, 00040E28)
Starting backup copy via pg_basebackup for 20180715T114042

The database is empty ( a new one) but still it doesnt finish...
Any idea why ?

I think that 4 and 2 are connected. Any idea guys ?

Thanks , Mariel.