One of the ways to determine when we have reached the End of a Hand or reached the Flop is by looking for the visibility of a hole card. It is also used when using the Move To Grid setting = "When dealt cards".
However, there is a specific problem with this: It depends on your hole cards being in the same location on every table of a particular site.
During Include Site setup, SaT asks you to click on the white part of your hole card. SaT will save the click location, and when needed it will search for the visibility of your hole cards at that click location. Suppose during Include Site setup, you were seated at the top of the table, and clicked on your hole cards at the top. If you are NOT using preferred seating, then perhaps at another table you are seated at the bottom of the table, SaT may incorrectly not find your hole cards, since it will be searching for your hole cards at the top of the table (where you told it to during Include Site setup) instead of the bottom (where you are currently seated).
To solve this problem, we utilize the preferred seating option of the poker site. This will ensure that at every table, we sit in the same seat. That way, SaT will always be searching for the hole cards in the correct location.
However, even this isn't perfect.
You can still run into trouble if you mix different tables such as 6max, full ring, or heads up. Because of the different number of players at each table, the preferred seating might not line up in the exact same location. Take a look at the image above. All six seats on the 6max table line up perfectly with the 9max table. So if you mix and match 6max and 9max on PokerStars, and make sure your preferred seating for both 6max and 9max are the same seat, then you should have no trouble. But, then look at the 10 player table. To make room for the 10th seat, all the seats are now shifted. No matter which seat you choose, it will not line up with the 6max or 9max table. It looks like the closest seats that line up on all three 6,9,10max player tables, would be the 2 and 9 seats on the 10max table, near the dealer chip tray. So if you plan on mixing all three table types, then you would probably want to try those seat locations.
Because of these complications, Hole Card Detection is turned off by default. I thought about not offering it altogether, but some people have requested it in the past. As long as the issues are documented for people to understand, it should be ok. As mentioned above, the only problem that you would run into is having tables prematurely returning to the stack instead of staying in the grid. SaT will be thinking that the current hand is finished and then send the table back to the stack. If you suspect that you are having this error, you can verify it by turning on the End of Hand notifications in Advanced Options, and seeing if the notification is occuring at the wrong time. If so, then you can try to fix your seating and re-include the site, or simply turn off Hole Card Detection.