Yup, individual parts, each joined as a group/component, are the way to go if you want to make sure the parts fit, see true shape and dimensions of each part, and do redesigns.
Grouping is best for most stuff, but if you have a part exactly duplicated a few or more times (examples: joysticks, leveler feet), use component instead. Edit any one of the component copies, and all of them are edited.
I haven't used layers yet, but I really should be.

IOW, if you don't to do layers, you don't need to as long as you group/component.
OTOH, if someone just wants the outside look, say for a fake arcade room instead of for cab designs, one block can be quicker.