Once upon a time when the game was much different I actually used the full 3 days. Arctic Future was the last age at the time, and the gain 10k happiness and gain 12k happiness quests were very appealing to up my quest-count with a not-so-high Chateau Frontenac. I was not yet at the end of the age with the Ice Flower to be able to just do the 8 deco quest efficiently (my CF wasn't high enough to support the costs of 8 tube entrances)
I had a sizeable portion of my city set aside to build (Bronze Age) Taverns, which with the construction boost would complete in about 10 minutes. A full set of taverns would get me 2 quests for up to 12 an hour. Taverns were chosen as a balance between construction time, construction costs, and number of clicks required. High age decos would've taken less time, but cost too much. Higher cultural buildings would take too long to build. Cheaper cultural buildings would take even more space (though I did consider them).
I got lots of curious questions about why I had 40+ Bronze Age taverns in my Arctic Future city, it was great
Oh for simpler times... These days if I had such a city I'd get a much different form of player interaction I expect - rude questions about why I was wasting so much space
(And to be fair, I wouldn't set aside that much space anymore for it even if it was the only option to increase quest count - and in my AF world I have a high enough CF that I could do the 8 tubes and 2 unbirthday-style quests in AF til I unlock the iceflower - and use 500 culture FE decos in the case I want to do the happiness quests)
Since then the main purpose for the construction boost has been for rapid barracks switches where I want to get them up and producing troops for GvG (also something I haven't done much in a very long while). I'd use the construction boost to make the time reasonable and then recruitment boost to crank out many sets to fill DAs. For which purpose I'd kill for a shorter duration because as mentioned earlier, I just need it long enough to start the constructions. (When I was doing this, i'd typically buy a cheap short throw away buff in slot 1 so I could park the 3 day construction boost in slot 2, and still be able to use slot 1 without paying 50 diamonds daily)
I could see wanting a multiday version in a very early city maybe because you might need to actually build houses, wait for them to complete, and then build what you wanted the population for. But the chances that you've fully unlocked your tavern to have the big boost, and yet still need to build houses to build something else (i.e. haven't won any event pop sources yet) seem very low.
So overall I'd be in favor of shortening its duration, or having the option to cancel buffs at will (though they've nixed that before I'm pretty sure since they want to pressure you into paying 50 diamonds for the second boost).