So, why would you use a Tool Preset to save your brush settings, rather than a Brush Preset?
Dave,
I'm not saying anything that Chris hasn't already said, but perhaps this will help.
A Brush Preset contains just the information in the brush palette. This defines the brush tip and behavior characteristics, but does not define settings such as color, mode, opacity, or flow. When you change Brush Presets, these other settings will not be affected and will stay the same.
A Tool Preset, on the other hand, can contain all the tool settings. For a brush, that includes the information in the brush palette and the other settings for the brush tool such as color, mode, opacity, and flow -- saving the current color in the preset is optional. When you load a Brush Tool Preset, the current brush tool settings will be replaced by the settings saved in the preset.
Tool Presets are useful when you want to save an instance of a specific brush.
Say you frequently use a particular brush in multiply mode with airbrush selected and 40% flow. Save it as a Tool Preset and you can reload it with those specific settings whenever you need it. Check the "Include Color" box and you can even save it with a specific color. You can't do that with a Brush Preset.