I have access to my daughter’s college portal - have done registration and housing selection for her when she was otherwise occupied during her time slot just like twoinanddone - it has come in handy.
My daughter gave me her login info because she was too lazy to go thru the steps to grant us parent access and didn’t see the point. I only use it to pay her bill. Though this gives me access to all her assignment and test grades I’d feel way to stalkerish looking at those.
I have access to my sons portal. Since I pay the bill on there I can see all the information. It is true that most professors do not post any grades until the final. I didn’t check his grades until he started to have some problems in a few classes. If I do look I try not say anything until he mentions it.
We never talked about grades at the college level, but then again, I resisted looking at report cards in elementary, middle and high school 
Before college, I could tell who was working hard in my house, and it wasn’t always the one with great grades.
At the college level, they will end up on probation if they are not doing well, and I guess I would want to know that. I relied on other methods, rather than grades, to see how they were doing, like visiting or phone calls. I did not ask about grades but in the course of regular conversation just wanted to make sure they weren’t depressed or having trouble concentrating etc. One time, on a visit, my daughter revealed she had stopped going to a class-long story- and she needed to deal with it administratively by withdrawing. She wasn’t really up on policies. By junior year she knew how to do these things promptly.
The real value lies in communication to avoid a bad grade rather than see it after the fact!