Could you elaborate on what you mean by 'understanding' of the music? I think I understand what you mean to a certain extent -- when I play Beethoven or Chopin, I get a very good feel for the music, I can hear the beauty and emotion within it, and I can express it quite well. But every Bach piece I play lacks the emotion, the grace of other composers. Although it's complicated music, it just sounds mechanical to me, therefore it's hard for me to find an 'understanding' in it - as such, drilling the bars over and over until I have the music memorized has been the most efficient way of practice I've found.
Esse aut non esse, quod dictum est:Utrum iam nobilior in mente patiDe fundis sagittisque detracti in insana FortunaAut arma capere contra mare angustiae,Et contra eos usque ad mortem, somnumAmplius, et per somnum, ad finem dicimusCor-DOLOR, et mille Natural shocksQuod caro heres? Iam consummatioPie esse voluit.
To be, or not to be, that is the question:Whether 'tis Nobler in the mind to sufferThe Slings and Arrows of outrageous Fortune,Or to take Arms against a Sea of troubles,And by opposing end them: to die, to sleepNo more; and by a sleep, to say we endThe heart-ache, and the thousand Natural shocksThat Flesh is heir to? 'Tis a consummationDevoutly to be wished.
Comprehension or understanding makes it a whole lot easier to remember and recall the passage. When one understands what is being said, one can also summarize and put into one's own words the gist of the idea.