I mostly only use tickets offices when buying tickets not available online, like railcards, car park seasons or photocards or when needing to pay with a Rail Travel Voucher (I still get them, despite asking for a cheque/cash).
The main reason is that I've had too many issues with difficult staff, such as:-
- Telling me the ticket I want to buy doesn't exist (a return from my local station to London Zone 1, which is cheaper than the Peak Travelcard they try to sell you - I only need a return not so a Zone 1 return is sufficient). The South Western Railway website will sell you such a ticket, as will the ticket machines. Just not the ticket office.
- Not selling tickets for tomorrow until after 3pm (yet I can buy a ticket for any day within the next 3 months from their website and immediately collect at the machine - so why not at the ticket office).
- Refusing to sell off peak tickets at peak times (even after you have explained you are not wanting to travel immediately, e.g. buying a ticket for travel after work on your morning commute)
- Making a fuss in selling tickets originating at another station - sometimes insisting on seeing other tickets (season) that I will use to get to the station I'm wanting to buy a ticket from before they will issue the ticket I asked for.
- Being unable to find the ticket I want (a particular problem seems to be tickets with PlusBus extensions)
Generally I buy online and collect at the machine.
On one memorable occasion when trying to claim void days on my season ticket, after much huffing and puffing I was handed a form and told to fill it in. But given no pen to fill it in with - I asked for a pen and was told he didn't have one (I had to borrow one from someone else in the queue).
In addition buying a ticket online usually means you can get some sort of discount or other incentive (e.g. Nectar points), which are not available when booking via a ticket office. You can also choose your seat on many websites which again most ticket offices don't seem to offer (usually ticket offices seem to be able to offer window, aisle, airline or table, but not a specific seat).
Generally when arriving at a station and wanting to travel immediately i'll use the machine unless there is a queue for the machine and none at the ticket office.