I don't have to do any of that in Photoshop. Tilesets are 256 pixels big. set that for width, pop in any random number for height, I like 2000 to start with. Set grid to 32x32 pixels. Boom start working. Nothing to calculate. Need more height? use crop tool, select whole area, then drag it down past the bottom of the image, 'crop', it adds to the image however much you pulled down. finished? crop it back down. Can't align something right? there's a snap to grid' and an align option (align right/left/center/top/bottom).
There's no math, no cutting images out. I don't grasp what you mean by taking a screen shot, only time I need to do that is when making a custom menu and I need the x-y cords to place things and photoshop also gives you that just by hovering your mouse over the image.
So yeah, I would use it over Photoshop, it's a lot quicker and easier and I've used it for years. CS4 makes it even easier. It's even fantastic for pixel work and I do all that in it as well.