Historically, it was generally-speaking, cheaper to book in advance. But, with the elimination of change fees and other enticements, RM/IM is much more difficult. Thus, it makes all the sense to plan a trip to the UK, but little sense to book and pay. While a refund is in order if the flight is cancelled or significantly changed, a good chance that the changes are not significant and thus, if one does not wish to travel or is unable to travel, one is stuck with what amounts to a credit or rebooking for use on the carrier of choice for a later date.

Other carriers or destinations might be more useful and circumstances may change and the prospect of having made a long-term interest-free loan to an air carrier may not be the best investment.

So maybe the best way to look at this is not to book anything which is not fully refundable (at this point).