What are the problems associated with purchasing an Italian standard SIM card?

Performance
All standard data plans have low or medium priority to the operator’s antennas, and if your area is congested, your speed decreases drastically.
Also if they indicate “unlimited”, some data plans reduce speed after a specific monthly limit.
In some cases, tethering is prohibited.

Contracts
Depending on your home country, it may not be possible to sign an Italian data plan contract, for fiscal reasons. You waste your time in a store, have to talk with store personnel who may not speak English, and you have to sign (and understand) a contract in Italian.

“Add-value services”
Generally, standard data plans let you activate (and pay) for “add-value services” if you click on “fraudulent” banners. Our data plan does not allow you to activate any “add-value service”.

Hardware compatibility
If you bring a smartphone or a wifi router from your home country and try to use it with an Italian SIM card, you have to configure it, and you risk that the hardware is not compatible, because connection frequencies change from country to country.
In this case, you have to purchase an Italian device, which consequently will not work once you return to your home country.