Every manufacturer's image stabilization system is patented, so there is bound to be some variation in their function and effectiveness from brand to brand. It's also been an evolving technology, with some notable improvements over time.
For example, many Nikon shooters think that VR slows autofocus slightly and there seems to be some evidence to support this, so some folks choose to turn it off at times for that reason. Personally I use Canon gear and after fifteen or more years using a variety of lenses with it (nine currently), I think their IS system actually helps autofocus perform better... but I don't have any way of measuring this or any evidence supporting it.
Some systems also draw more power than others, so someone might choose to turn it off for that reason, too.... to conserve their batteries. I really don't see very much power used by Canon IS, in particular... using two cameras alongside each other, one with an IS lens and the other with a non-IS lens, I get almost exactly the same number of shots with them.
Also, some forms of stabilization react poorly when there's no movement to correct, going into sort of a feedback loop where they actually cause image shake blur. This is usually limited to certain earlier systems used in particular lenses. For example, out of around 3 or more Canon IS lenses, I know of five where the IS needs to be manually turned off if using the lens on a tripod and fully locked down, eliminating any and all movement. Other Canon lenses "self detect" and turn it off themselves, when there's no movement to correct. (This also conserves battery power, of course.)
Other folks simply turn off image stabilization when they don't feel its needed... when shutter speeds are adequately fast. Maybe they do that because of the slight noise it makes. Some feel that "locking" the lens elements may make for sharper shots. But some of us like that it also may help stabilize what's seen in the viewfinder and that can be helpful when using long focal lengths and trying to photograph distant, moving subjects.
How much "assistance" image stabilization gives varies from user to user. Older systems typically claimed two to three stops of assistance. Newer ones are claiming three to four stops... a few even five stops. But the user's skills and abilities, camera settings, local conditions such as wind or vibrations from a running motor or the rolling deck of a ship and other factors come into play. Basically, you have to determine how much help you get from it yourself. Do a series of test shots.
The longer the lens focal length, the harder it is to hold steady... Hence zooms will rely less upon stabilization or just be hand-holdable at slower shutter speeds at shorter focal lengths, but will require higher shutter speeds at longer ones.
Also, higher magnification such as macro lenses is more susceptible to shake blur, so stabilization is less effective. Most systems give little to no help at full 1:1 (life size) magnification or higher. They can be more effective at less extreme magnifications and give their maximum potential at greater distances.
Finally, it's important to keep in mind that while image stabilization, good technique and a steady hand can allow amazingly slow shutter speeds to be hand held... It does nothing
to stop subject motion blur effects. You still need a fast enough shutter speed to freeze subject movement, if that's your intention. Exactly how fast shutter is needed varies depending upon the speed of the subject, the direction it's moving in relation to the photographer and the distance from the photographer. For example, a subject that's relatively close and moving quickly from right to left (or vice versa) across your field of view requires a faster shutter than one that's heading directly toward you from some distance.
To better understand what's happening with sales tax collections for online purchases, see: https://www.nolo.com/legal-encyclopedia/50-state-guide-internet-sales-tax-laws.html
But, basically in June(?) 2018 the US Supreme Court reversed it's earlier decision regarding out-of-state sellers being required to collect sales tax. Used to be prohibited, but now it can now be required. The Supreme Court stated that each state has to pass specific laws regarding the process and there's a great deal of variation from state-to-state. The amounts to be collected and the implementation of the taxes of online sales differ by state. It's a mess and has got to be driving online retailers crazy!
In the past, out-of-state retailers had an advantage over local brick & mortar... being able to offer products to people slightly cheaper by not charging sales tax, while the local retailer was required to collect it. Actually, most states with sales tax have laws that require people making purchases online from "remote sellers" are supposed to self-report and remit the appropriate amount to the state sales tax collection agency voluntarily. However, I bet a lot of people fail to do so (not that anyone would or should ever admit this in writing in a public place like an online forum). There also appear to be some challenges to the recent court decision, so things may change again. We'll just have to wait and see.
Sales tax is not something to be messed with. A friend here in California has owned a busy photo studio for many years. Turned out he got some incorrect advice and wasn't collecting sales tax at times when the state felt he should.... Ended up with a bill for $600,000 for accumulated back taxes plus interest and penalties for failing to collect them! Took him years to clear up the problem.