Ignoramus32423 fired this volley in
:

Oh, and why would LM317 waste less energy as heat?

It would not. It's a linear regulator, also, and disspates exactly
whatever is the drop*current across itself.

But it's darned handy for 'tuning' stuff.

There is a way, with an LM317 to get a 'soft start'. National Semi shows
a circuit or two that does that.

Having that constant-current output on the reference lead can give you
interesting possibilities.

LLoyd