You raise a good question, Underdog.
I continue to keep track (checking a website that allows me to see how many days it's been, whenever the mood strikes me). If I stopped doing this would I go back to smoking cannabis? Not sure.
When I tried to quit in the past, I kept falling back into daily use after telling myself to use only on special occasions. The day count thing (or week, month, year count, if you prefer) reminds me of just how far I have come. It feels like a heavy weight (in a positive way) of good choices that have accumulated over time. It might be something like celebrating an anniversary to a significant other. If you fall on hard times, you might think twice about throwing away a 15 or 20 year marriage (compared to a 3-6 month marriage).
Agreed, anything taken to excess can be problematic. I can recall back when I first quit feeling particularly attached to my "day count". It was helpful to be able to compare notes with other quitters -- although we're all different -- about what I was experiencing at each stage of "recovery".
Unsolicited information here: some timelines that I experienced -- 30 days, feeling better; 6 weeks, quite an improvement; 6 months, even better; ONE YEAR - felt like I was totally "back to normal". Everything beyond about one year off cannabis has been subtle improvements, most likely driven more by lifestyle changes (and mental/emotional changes facilitated by being free from addictive habits) than by anything directly related to cannabis use.
Personally, I keep counting milestones because it feels like an achievement. Do whatever works best for you!
WL