as to why - MyISAM is an older storage method for databases that has a slew of issues such as bigger hangups for messing with the data (table locking vs row locking), and worse off: bigger potential for data loss in the event of a crash. if data gets corrupted your in trouble which we have had one corruption incident before
additionally, myisam apparently requires routine 'maintenance', that I did not know about, so needless to say we haven't been doing it... But InnoDB is newer and doesn't have many of those flaws.
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