You can sign documents with the click of a mouse on a desktop. The validity of a digital signature comes from an authenticated account, time stamps, and an encrypted key; not your finger tracing on a touchscreen.
Not every digital signature is legally binding, I’m afraid.
In my country, there are 3 types of it. A simple one (login/password), unqualified (encrypted series of numbers), and qualified (same as unqualified, but encrypted using certified means by government). The last two are stored on a physical drive.
The higher the grade, the more legal power the signature holds.
When signing it by hand from a tablet it’s the same as signing it personally where I live. Which, unlike qualified digital signature, can be used for any document.
That’s actually something we need to get handled as a society. Unfortunately the justice system still runs on fax machines so we’re basically not viable as a species.
By that logic, a tablet is exactly the same as a laptop, just more portable.
SkyeStarfell already said it more politely than I was going to, but you can also sign things from phones. The point was that it doesn’t have to be a written signature so the tablet medium provides no benefit.