Power treads give +9 to either Strength, Agility, or Intelligence. You can switch between the "active" attribute. When buying them for my hero, the default thing I'd do is set them to my hero's primary stat.
Casters of professional games often refer to "Tread Switching", which I assume means changing the selected stat during the game or even in the heat of the moment. I'm guessing (partly from the related gamepedia article) that this is mostly done to affect regen items like a bottle. I also figured that perhaps setting it to Strength when being chased (for those few extra HP) or to Intelligence to bump up those few points of mana to TP out are valid uses (or are they?).
This leads me to the first part of my question: what exactly is Tread Switching?
Whatever it precisely is, it uses APM and requires some attention, both of which you don't have in surplus as a low(er) ranked player. I'm personally around 3k MMR, so for me it competes with -say- checking the mini-map and hitting/missing a last hit or two. So I'm not even sure how to decide if it's worth spending APM or attention on it.
So this leads me to the second part: how worthwhile are the effects of Tread Switching?
Best Answer
I'll answer in reverse:
How worthwhile are the effects of Tread Switching?
Miniscule, it's a micro-optimization and not needed unless you have spare APM. Better to focus on strategy, map sense and team communication. If you do wish to do it, it's more useful early game rather than late (percent of your total stat pool shifting)
What exactly is Tread Switching?
This is down to dota2 mechanics being copied over from WC3, and it's an arbitrage between percentages and absolutes. Skills commonly use an absolute amount of mana, ex. 100 mana cost for a skill out of say a total mana pool of 500.
Say you are current on STR treads and on 100/500 mana. What happens to your mana total when you change to int treads? Int goes up by 9, each point of INT gives 13 mana, so your new max mana pool is = 617, your pool is also scaled -> 123.4 / 617 now. Voila, you gained 23.4 mana, which you could use to cast a spell.
So skills commonly consume mana in fixed amounts and regens (clarity, soul ring, arcane boots etc.) replenish mana in fixed amounts, while any changes to your mana pool happen in % fashion. By changing your mana pool inbetween casting and replenishing, you can gain an edge. It's not too big with treads, but it can be bigger with arcane boots + soul ring...
Ex. if you're not 500/1000 mana with arcane boots + soul ring. Use of soul ring -> 650 / 1000 or 1. Drop arcanes -> 375 / 750 2. Use Soul ring -> 525 / 750 3. Pick up arcanes -> 700 / 1000 (+50 mana by comparison)
Just one more in the list of intricate mechanisms that can take your individual skills to the next level. But not before map sense, item sense, last hitting, stacking, orb walking, learning about vision and juking in fog, dodging projectiles and a whole lot more :) That depth is the fun.