Reasons for disabling statistics auto update?
My advice:


Leave 'auto update stats' on (until you run into a very good reason not to) - you don't want a big delete in middle of a day to throw off query plans until the next time you run maintenance.
However, schedule index maintenance/update statistics at a quiet time. sp_updatestats will update all stats for all tables in a database for you, but that will also cause stored proc recompiles, so choose your time carefully (i.e. sp_updatestats right before your end-of-month reporting is probably suboptimal).


How often you need to run index maintenance/rebuild stats depends on your database load, specifically how often your data is modified (i.e. INSERT/UPDATE/DELETE). If you're modifying data all over the show (i.e. a staging table for a weekly batch process), you probably want to update stats/reorganize indexes nightly. If your data is rather more static you can probably make it a weekly or fortnightly schedule.