Features of series and parallel combination of resistors

[agnibho]

Homework Statement

Give the features and the utilities of the series and parallel combination of resistors.

The Attempt at a Solution

Series combination:-
(i)The current has a single path for its flow.Hence the same current passes through each resistor and so the potential difference across any resistor is directly proportional to its resistance.
(ii)The potential difference across the entire circuit is equal to the sum of potential differences across the individual resistor.i.e.,
V = V₁+V₂+V₃+...
Parallel combination :-
(i)The potential difference across each resistor is the same(=V_a-V_b=V,say) which is the equal to the potential difference across the terminals of the battery(or source)
(ii)The current in a resistor is inversely proportional to its resistance. The sum of currents in the separate branches of the parallel circuit drawn from the source.i.e., I=I₁+I₂+I₃+...

These are the features I managed. However I would like to know the utilities of these two combinations.

 

[da_nang]

Which would you use to a) increase resistance and b) decrease resistance?