Vidiš, nisam toliko razmišljao o tome od silnog oduševljenja kada sam slučajno naleteo na tu foru posle dužeg neuspešnog traženja i to u manual-u.
Evo ovde primera korišćenja sa razlozima za i protiv:
http://www.mysqlperformanceblog.com/...innodb-tables/
Zaključak: Should you go and change all flags to use this approach (CHAR(0))? I do not think so - for most applications using TINYINT, BIT(1) or ENUM for flags benefit would unlikely be worth the trouble. Due to complication I also would not recommend as a base approach for new applications. However in special cases if you have very many rows and very many flag values to deal with which you can't pack to the bitmask this approach can be quite helpful.