On one hand, limiting the magic has many uses. You can keep it dramatic and wonderful that way. You can keep it from giving your characters too many easy techniques to get around the obstacles.
On the other hand, plentiful magic does help with the world-building if you want to avoid an ugly realistic pseudo-medieval setting. Any sufficient advanced magic is indistinguishable from technology -- except that you can make it feel like magic, with all the potential of wonder there. You can make the world itself entirely filled with wonder. And it does help with the Mary Sue, whose problem is often that she has magic, magic, magic! and no one else does. Plentiful magic means that your hero is not a special little snowflake just because he has some, or even a lot. And your villains can load up on it, too, giving him more obstacles that he can't get around.
From my random inspection of the fantasy field, it seems that the first set of advantages works better; books with low magic tend to be better. Maybe I just have an odd sample.
What are your favorite high and low magic worlds? Do you think one of them works better -- and why?