trying to understand assemble option in mdadm please help.

[Muhammad Yousuf Khan <sirtcp@gmail.com>]

apart from my question i know what does "assemble" mean but most of
the time it create conflict with the option "add".
for example.

if raid is broken then i can just re-add the the broken partition

if my HD fails then i will add the new drive, recreate the partition
and add it to new array and cat /proc/mdstat will show me the sync
status.

but now the next question coming in my mind is why assemble.

i also observed that some time when i restart the computer contain
RAID1 after 2 or 3 months it start to test or (maybe)assemble one of
the partition by saying that (more or less) that the raid has not been
tested for this this days so now reassembling (sorry if i am wrong
since i can not recall the whole message)
so the point why assemble is necessary?

if assembling is that necessary then why should i wait to restart. i
can do this manually every week or can schedule a task for it.

Thanks,