Max price vs extra usage

[#1]

I'm on BBYW Option 2 (15 GB per month). Due to a new internet radio and the release of the new software version of crystal meth (COD MW2) I expect to need more usage this billing period. Question: what's the difference between adding, say, 3GB to my account and setting a maximum price on my account? I see both options are available and am not sure which is the right way to go.
Thanks.

[#2]

Hi there,
It works out a little cheaper to add usage in advance rather than setting a maximum price (75p per GB pre pay vs £1 per GB post pay).

[#3]

ok, thanks. If I add extra usage in advance but don't actually use it do I still pay for the full amount  I added? e.g., I pay in advance for an extra 3 GB but only use 2GB, do I still pay for the 3 GB?

[#4]

Yeah, whatever you add in advance you pay for, whether you use it all or not.

[#5]

Depending how much extra you need it may be better to swap to BBYW option 3 for this month.