I basically use them when I have a huge task at hand bigger than the Android smart phone but I do share hotspot through the phone to my laptop.
If you regularly share your cellphone network with your laptop, maybe consider buying a dedicated USB modem instead. I've heard that hotspot sharing for a long time can degrade your battery quickly since it makes your phone too hot. It also affects your phone even if you use a USB cable to share the connection, CMIIW.
The problem with smartphones is that it's easy to touch with fingers wrongly, what disturbs and annoys the gambler during his game's session a lot, besides being dangerous to touch somewhere by mistake, placing a wrong bet size. Also, it's not possible to see the whole page on smartphones, so you need to scroll a lot of times, and any call or notification the gambler receives meanwhile is going to distract him and overlap the casino's site or app. Desktop, on the other hand, is like a complete control panel where you can track and control everything with much more accuracy and calm.
Touching the wrong thing can be solved easily by a confirmation dialogue, even though I doubt any website will place such a thing on their website for every possible action that the user can take. That being said, most phones have larger screens nowadays, so a user can switch their phone if a mistouch happens regularly. As for the UI, I heard most websites support mobile view nowadays, so if your preferred platform still doesn't support it, maybe they need an update. Sometimes a developer would just release an app though.
If you connect the internet connection from your cellphone to a computer using WiFi, I think the internet speed depends on the network on your cellphone. But it will be different if you use a special connection, such as subscribing to the internet using a LAN cable provider. The speed will be faster using a LAN cable, but it depends on how much speed you get from the provider.
The WiFi device itself might affect the network too, but I don't think it's easy to find such devices. Most laptops and phones nowadays support WiFi AC (even AX), and mobile phone networks even at 5G probably won't top the bandwidth at all, unless you live in a very technologically advanced place. CMIIW.