50% of the time Vnav to the runway, flap selection will dial back speed bug and meet all constrants...when cleared to descend or cleared for an approach make sure you put field elevation or you will lose path to the runway...back to pilot stuff then. Lnav / Vnav approaches are about the laziest if you are the PF...just call for flaps,gear and checklists. Assuming you have autothrottles. B737NG. PHX Eagle1 Star is better if flown Lnav/Vnav. ATC will give you descend via the star, perfect.
problems come up with poor winds aloft or strong tailwinds on a star, level change works well then. 10-6 software has a glitch thats called Energy Conservation. humm 10-6a will solve that. When I see it dialing back speed I hit speed intervention and start looking for why.