Growing a day streak teaches consistency and resilience.
As a master streak-breaker who just attained a 500-day streak on Makerlog, I know it all too well.
Sticking to the same habits for several days takes planning, discipline, and mental strength. But it's not nearly as important as learning how to get back on track when you fall off the wagon, or as Rudyard Kipling says:
If you can make one heap of all your winnings
And risk it on one turn of pitch-and-toss,
And lose, and start again at your beginnings
And never breathe a word about your loss;
It takes a different kind of fortitude to recover from a loss: acquiring momentum is much harder than maintaining it, which is why it's easier to come back to the gym if you already did the week before. The longer you wait, however, the stronger the resistance.
I have huge respect for people following Kipling's adage.
A streak is a tool to develop a habit, but past a certain point, it has to become a tool to support deliberate practice.
Deliberate practice is not mindless repetition, it's continuous improvement. You still do one activity a day, but you have to strive to be better than the day before.
Keeping a streak for the sake of it without questioning its purpose isn't going to add anything substantial to your life, you might as well break it and learn something from it.
Having a huge streak is definitely a big ego boost, and it can help you keep going when you feel like you're not making any progress. The problem, however, is that it's not an accurate metric to represent your internal progression toward mastery.
You need something more. You need to see beyond the streak to deeply fall in love with the craft. This is what will ultimately keep you going no matter what.