i did BIAB for a while, until i built my single-tier. i liked BIAB and made and great beer (IMHO). Jamil likes to point out that the one drawback of the process is that you don't recirc/vorlauf the wort so it's more cloudy than traditional mashing. i'm not sure how important that is, tho...
traditional BIAB is to use all your water from the outset. i never did that. i always mashed with 1.5-1.75 qt/pound, then used the rest of my water for a batch sparge or two. definitely increased efficiency.