Transient Eye has posted an excellent piece on how sensor size affects various camera systems. It’s framed for street photographers who generally don’t do much shallow depth of field work and so, the advantages of full frame cameras are lessened.
For better or worse, the 35mm film format has become the standard against which all other file/sensor formats are compared. But understanding how to achieve identical images from cameras with different sensor sizes – i.e. images equivalent to a 35mm “full-frame” camera – is very useful if you use several different formats.
The diagrams are, if nothing else, a great way for those who don’t understand “crop factor” to finally get it.