Janelle, where are you staying that you call west?
The main benefit of buying Advance tickets several weeks before travel (buying ahead is not the same thing) is that they have discounted prices and included is a preferred seating position, Advance fares are priced dynamically, as they sell out prices increase, when they're gone they're gone,
Not all routes have Advance fares or seat reservations.
Disadvantages are, you are tied to a specific train time, you will be clock watching, if you're having a nice day out and want to return later you'll have to cut it short, if the weather mis behaves on your chosen day your are still committed to go, if you want to change your plans late on, you are stuck with the tickets,
There is something called Groupsave for off-peak walk up tickets, an automatic discount for I believe 3+ travellers,
There are various 12 month concession National Railcards (16-25/senior/two Together/disabled)you can purchase, but for short visits and few train rides they won't be viable, some have peak time restrictions too.