Memorizing is the best but if you are in a variety of situations where you need lots of different types of music it can be hard. Not doing a song for a while will cause you to lose it from memory. If your doing a lot of the same thinga on a regular basis I'd say yes, memorize your setlist.
I love using my IPAd but I still keep a regular book of tunes for solo piano jobs.
Now if I could only learn how to change setups on my BK9 along with song choices I'd be a happy guy.
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Bill in SC --- Roland BK9 (2) Roland BK7M, Roland PK5 Pedals, Roland FP90, Roland CM30 (2), JBL Eon Ones (2) JBL 610 Monitor, Behringer Sub, EV mics, Apple iPad (2) Behringer DJ mixer