Best use is when a school has a firm/sound Assessment policy and uses all the AM functionality to the full.
Here is a quick list of how we mainly use AM:
Creating 3 year subject specific and school specific regression (Progression) lines for use in the AM Prediction formula to generate Indicators/Targets.
Showing all historic data like KS2 SATs, CATs, FFT, last academic year's grades and target comments, whilst having all this year's reporting home grade columns available inc. Indicator/Target (see previous) and traffic-lighted "Progress" columns etc. etc. etc.
HoD course marksheets with similar.
Performance Leader (vvertical House) marksheets with similar.
Columns for flagging up importance of meeting parents at Parent's evenings etc. etc.
Departmental marksheets (big job but well worth it) cleverly linking ongoing assessments to the more categoric reporting home grades. The latter goes down well with teachers who do not wish to duplicate things. Needs coordinating at HoD level though.
Range of individual reports for Reports to Parents, Exam success interviews, for student showing projected grades & Indicators for their ROA/Personal Profile etc. etc.
Performance Analysis used for instant value added graphs for current students as well as reflecting back on last summers results; this by cohort, year group, class etc. etc.
Chance Analysis proving particularly useful in terms of Key Stage Progression, again for year groups, classes, SEN, AUDG eg "GradeWatch" etc. etc.
Profiles for extended text reports, drawing in useful grades/marks even reading age for example.
Huge longer term benefits from having AM individual Reports & Profiles available via Document Management Server
Could go on and on but part of the firm/sound policy is to include data entry that is valid, accurate & reliable.
Next is to communicate school wide (arguably beyond the school if you include other stakeholders like parents, Governors etc).
Next is to ensure suitable intervention/support mechanisms. We have found a range of these is the way to go.
Finally, if you know what you want to get to but are concerned about how to manage introducing things, consider priorities, essentials, desirables etc. etc.
Some of my points have been mentioned in previous posts, never the less I hope it helps.