CMYK - Working Space
With the exception of the list of available profiles making your
choice of CMYK Working Space isn't that different to RGB. Again, having
Advanced Mode activated gives you a more extensive list. Since desktop
inkjet printers from Epson, Canon and HP actually require RGB data rather
than CMYK and so configuring this particular Working Space will have
little or no influence in their actual workflow.

Figure 6
As mentioned above, the choice for you make is pretty much irrelevant
if using a consumer class inkjet printer. In my case I just picked US.
Web Coated (SWOP) V2. We can also have pick the old Photoshop 4 or 5
default CMYK options, the ColorSync settings (Mac only), or even
customise our own settings.
Greyscale - Working Space
With the Greyscale Working Space we have access to two gamma settings,
a series of five pre-set dot gain curves, the ColorSync Grey Work Space
(Mac only) and the ability to customise the dot gain to our own
requirements. The screenshots below (figures 7 and 8) show the various
options and a typical customised Dot Gain curve.

Figure 7
Note that if you choose to use a Custom Gamma or Dot Gain this will be
the Working Space listed in the Grey Working Space pop-up menu.

Figure 8
A very important point regarding Greyscale is that it’s not tied to
the CMYK setup! This is why some legacy greyscale documents might not
look quite the same as they did in Photoshop 5.x (does anyone still use
Photoshop 5?)
Spot - Working Space
The Spot pop-up menu is broadly similar to the greyscale, but for spot
colours. The options that we find include a series of five pre-set Dot
Gain options and the facility for customising the Dot Gain curve if
required. In my case I simply selected the standard 20% option.