[denny]

You can definitely increase your efficiency by sparging more, but it can come at the expense of beer quality.   Remember, you have to thin in terms of both conversion efficiency and lauter efficiency.  You can have poor conversion efficiency but sparge more or great conversion effieincy and sparge less and still end up whit the same overall efficient.  But the wort that's produced via a higgher conversion effieincy will be of a better quality.  For more info, see...

http://braukaiser.com/download/Troester_NHC_2010_Efficiency.pdf

[Will's Swill]

The 1.5x was probably intended for fly spargers, for batch sparging it may not make as much sense.  But there's something to be said about having a consistent method of sparging, so that your mash quality and efficiency are always known within some tolerance.  Excepting, of course, if you're altering your mash/sparge schedule based on style.

[Kirk]

A lot of that 1.5 is going to stay behind in the MLT, never making it to brew kettle heaven.

[Will's Swill]

Then that's a poorly designed MLT. 

[morticaixavier]

Then that's a poorly designed MLT. 

not if you are fly sparging. You never want the liquid level to drop below the grain bed so you keep adding water till you get your boil volume in the kettle or the SG of the runnings drops below the desired level

[Will's Swill]

I do fly sparge.  And I keep my liquid level above my grain during the sparge, but then I let the last of the sparge drain out of the lauter tun.  And I use the same amount of sparge water per pound of grain independent of target volume.  That way I never under- or over-sparge (assuming that my sparge amount does not cause over-sparging) and my wort quality and efficiency is reasonably predictable.  I avoid checking the gravity of the runnings by acidulating (acidifying?) the sparge water to prevent tannin extraction.

Your way works, too, but then most of the 1.5x will make it to the kettle I would wager.