First, it is worth mentioning that there are several models for authorship in use. In some fields alphabetaical is used, in some the last author is considered the important person (usually project leader), in some single author is used even when collaborations are performed. That said, however, the most common form is by weight and I mean weight in an ambiguous way because this is what is usually the problem, weight can be input but also importance or even by bullying.
So, the way in which to judge placement in an authorship list has shown signs of collapse, not to mention inflation. To remedy this many journals start to ask for accounts of the contributions made by each author. The notion of contributorship rather than authorship is emerging (see e.g. the BMJ description of their use fo the terms in practise). The ideas are based on the (expanded) Vancouver Protocol definitions of authorship which is as follows
- Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work;
- Drafting the work or revising it critically for important intellectual content;
- Final approval of the version to be published;
- Agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
This has been reproduced numerous times in replies on Academia.sx so you may want to do a search on the authorship tag and on the term contributorship to see more discussions.
So as the idea of contributorship and the definition of what contributions mean the view on author order might become closer to what it originally was intended. There is thus good incentives for listing contributions in paper even if it is not requested by journals. My suspicion (any certainty will have to come with time) is that when publications are assessed for job applications and promotions, the contributorship will be increasingly important, and by that coherence between author order (including appearance as author) and actual contribution.
In the end being high on the list is important, clearly showing author's contributions is necessary to judge the placement. This, I would argue, is particularly important for early career scientists.