Data transfer can be considered as consumption of allocated bandwidth.
If you have limited bandwidth and have vast traffic then your
website hosting may load very slow resulting in diversion of your visitors. In such case you can only opt for getting more bandwidth which may be expensive, so better way you should reduce your data transfer amount by building simpler more efficient
website hostings with well optimize graphics this will help in saving bandwidth.
So If you have a huge
website hosting with lots of graphics then you should have more bandwidth for faster data transfer.