I have recorded 'marital status at death' for years - going way back to PAF I just used to add info to person notes - but I treat only as a 'guide' as in some cases it might cloud the issue of 'further research' ie not married does not mean a person did not have children or a long term 'partner' as is common today, perhaps very unusual in the past but it did happen. I also have a couple of instances where a divorcee was recorded as single at death and similarly I found a divorced cousin recorded as single in 1939 register, perhaps preferring not to admit to divorce?. None the less I think its useful info to record!
The other place I have found the visibility of the Marital Status through time useful is when entering a marriage and either party is noted as widowed. If entering an individual/couple from a marriage registration I approximate the birth years as marriage date -18 years unless the registration document is more specific that 'Full'. In the case of a widowed person I revise this approximation to -30 years, although it is usually greater it places them in the timeline. Having the visibility of a person being widowed not only prompts me to search out the previous partner(s) but also their death(s).
We know Marital Status can also come from census records so having it noted several times in a persons life by date of event becomes useful, I can also sort the widowed on People View for further research. If you want to make use of such a statistic I would suggest something other than Notes for the data entry.