Not all tutors are bad, but there are some extremely bad ones marking the TMAs.
Sometimes It seemed like I lost marks for completely arbitrary reasons.
This one time I was deducted 3 marks for not presenting results in a table as opposed to just listing them. It was an L3 math module. You can guess how much value this piece of feedback carried when it comes to learning math.
I have also been deducted marks because of either carelessness or honest mistakes by the tutor. For example I made a reference to the method being used, but still lost marks for not making the reference. Once or twice I even solved the question correctly, but lost some marks as if the solution is wrong (with the given "correct" solution being the same as mine). I was able to get some of these corrected, but it's a real hassle to dispute TMA results, so I usually don't bother when I see that I'm getting enough marks for a distinction anyway.
Getting an answer from a tutor like this takes a week or more. They are not interested in going back and re-checking your TMA, so they are stalling. When you nag them enough, they will answer something like "No you are wrong, read page such and such of book X. Don't bother me with this nonsense I have too many TMAs to mark." I'm not even exaggerating this is almost literally what happened to me.
So far I had 2 tutors like this and 2 really nice ones who take time to read through your solutions and emails and reply quickly.