Frequency response is very dependent on impedance. Two very simple method used for finding high and low cutoff frequencies are the open and short circuit time constant methods. The way this works is that at low frequencies, internal capacitance of all transistors, etc. can be assumed to be open circuits. If one can then find the resistance seen by each external capacitance, one can find each pole in the transfer function. Additionally, at high frequencies, all external capacitances can be seen as shorts. If one then finds the resistance seen by each internal capacitance, one can find the other poles in the transfer function. Pretty much any resistance added within the circuit will affect the cutoff frequencies and thus the bandwidth.