Contrary to what BFSH said I find (found? ...it may have changed since I first discovered this) that when
approaching Starving and/or Dehydrated a dwarf will path to out-of-burrow food and drink. (Tiredness isn't similarly catered-for, as they'll happily lay down in the 1x1x1 burrow they've been assigned to for no apparent reason, when they decide they need some sleep.)
Anyway, I don't use Burrows with alerts, but tend to use them a
lot in peace and war alike for concentrating/directing the job-hunting process for
every currently non-military dwarf. Or perhaps, when I'm feeling happy-go-lucky, just the miners and select other professionals.
There's two approaches I've used to making sure that a dwarf is fed and watered and able to get to their bedroom, even while otherwise sequestered away in some specific workshop or at some specific workface:
1) Make a "food/drink/bedroom" burrow (or separate ones for each) and when I assign a dwarf to a burrow restricting them to a workshop/coalface I also assign them to this. (More flexible... I can unassign them from the 'living needs' burrow(s) to get them so spend more time at work, but then if you forget to take them out of the "living" burrow when you remove them from the "working" one it usually makes an idle and unproductive dwarf, until you realise.) As Alert burrow assignation is a single-burrow (I think), this method isn't open to you if you're an Alert-user...
2) For every burrow I make, include the food/drink/bedroom zones into the burrow as well as the workshop/whatever area. Does not need contiguous definition. When hungry they'll look for food within their burrow, when sleepy they'll (probably) look first for an assigned/temporary bed within their burrow. All I have to do is make sure each burrow encloses both areas. And I can redo later.
Burrows can overlap, as said, thus stone haulers can have mining-face and stone-stockpile in their burrow (regardless of what else there is) while block-makers can have stone-stockpile mason's workshop in their burrow. Block haulers can be 'confined' to taking blocks from a given masonry and putting them in a specific block-stockpile. Etc.
My latest fort has two "major" burrows. A "largely safe" area (all otherwise non-assigned adult males) and a subset "crèche" burrow that discourages the females (potentially nursing mothers) and all children from taking up jobs out in the open where snatchers can happen. This appears to work, so whether or not idle dwarves can idle
anywhere, my child dwarves are not wandering out in the open (and, moreover, onto the toxic sludge that
both of the major burrows exclude).
On top of those burrows I have (pretty much standard, for me) an "Exploration" burrow which generally a single miner is assigned to in order to define the advanced areas of mineworkings that I want
someone to explore (to find the limits to caverns, etc) and an "Infrastructure" one which may (although it varies) have every other miner that I have, in order to make sure that someone (or
several someones) is digging out the latest area for bedrooms, or water-supply tunnels, or whatever it is that my current fortress needs demand...
(It also lets me define a whole lot of
other digging, in advance, but by not using (or not assigning to) a mining-type burrow enclosing those areas they'll remain untouched. Before burrows I'd have been de-designating digging tiles on the border between "want to dig" and "don't yet want to dig", or make it an even more skeleton designation. But this way... blissful micromangement!)
What I'd
love to be able to do is to have "meta-burrows". Define burrows as currently, but with an additional option to "add <other burrow>" to each. Then a single "food, drink and sleep" burrow could be added/removed from the "exploration" or "infrastructure" or "block-making" burrows, on demand, without a lot of messiness. The "all inside", or equivalent, burrow could be defined by increasingly adding sub-burrows as new areas (cavern-fishing, magma-workshops, extra storage area, etc) get activated and given their own burrows, should that ever be my the way I organise things. Until then I manage. And... indeed... Manage. Intensively.
Oh, and back to it not being necessarily contiguous, burrows
don't stop wandering between jobs via 'unburrowed' areas. To discourage wandering short-but-dangerous routes instead of safer but more circumventing routes you still need to rely on the whole "Restricted pathing" thing down at the bottom of the (d)esignation menu. Or just ensure that the short route doesn't exist (which is generally easy, in my forts, in fact more or less the whole idea).