Hey Sandra,
I now personally redeem my MyPoints only for United Mileage Plus miles, as to me this holds the most personal value. But for many other people--- especially those wanting to save money on expenses, they redeem for gift cards.
Years ago however, I would redeem MyPoints for JCPenney gift cards to redeem them in store to purchase Jewelry when they'd have huge markdowns. You can use more JCPenney Gift Cards in store than you can online.
As to the timing, I'd redeem when I would have enough points for the max gift card, since most of the high value redemptions are the best values-- of course one should always do the math.
But again now I just redeem for Mileage Plus miles. [even though every 6 months or so MyPoints keeps increasing the redemption price for the miles]
-Max M