I was reading this neat summary of time travel rules in fiction and thinking about a couple of things basically angles and effort. The idea that a small change at one point leads to a big change in the future (aka two different kinds of things both known as a butterfly effect) predates modern science fiction. The proverb of consequences that typically starts with “for want of a nail” dates back to at least the 13th century and describes a causal chain of circumstances where a small issue (the nail in a horseshoe) leads to a major outcome.
Put another way: a small amount of effort in the past can lead to a result that would require a huge amount of effort if you were to attempt the same outcome in the present. I think that gives a neat rationale for fiction where you want time travel that allows changes to the future but where you don’t want an oops-I-stepped-on-a-butterfly-now-Donald-Trump-is-president situation.
If we see the initial act of time travel is the cause of the “future” change (i.e. the change to the present time of the time travellers before they set off) then we can (fictionally) say the amount of energy used has to match the amount of energy needed to change the original present to the changed present. So while a non-time traveller can make a relatively low-energy course correction to the timeline, a time traveller’s actions impact the future only as much as the same action would have changed their original present. So, for example, if a time traveller from 2020 stamps on a butterfly in the Cretaceous the net impact on 2020 can’t be any greater than stamping on a butterfly in 2020. The old ethical conundrum of going back and killing Hitler as a baby would then require you to (say) drop a comet on late 19th century Austria if you wanted to stop World War 2 etc.
Note that isn’t actual physics as it would require some kind of cosmic bookkeeping of energy but it might work as a tidy rationale for a time travel story in which there can be future consequences but not big future consequences.