If you want your micro to operate reliably from a battery or solar cell, SOME kind of voltage regulator/monitor is necessary anyway - move your watch under sun reflection from some glass building on a sunny day and you fried your micro with too much power. Now if you choose (or find) a "smart" one or a simple one, if you choose one that consumes 1uA or 100mA... it's all up to you (and the manufacturers...)