emmasdramas3:
Sometimes I for example start a show and rate it a 10, but if the plot isn't giving or it gets boring I just change it to a lower rating and it might turn out to be a show worth 7 stars.
Yes, ok you can do that because it's your way of doing things ... but until you change your ratings after full watch other viewers may not get accurate idea about show through ratings. Some people watch shows on basis of ratings. Suppose if 10 people start watching all of them gave 10 in the beginning, just to reset ratings after full watch ... don't you think it will be perfect 10 for that drama ... and others will believe it to be accurate.
emmasdramas3:
Even if the ratings were locked until finishing or dropping you could just mark it as completed and rate it straight away.
This part I agree too for older dramas... but in context to airing dramas it is not possible to mark them complete ... only drop. So yes, if you drop it there might be a reason, and you are free to rate and review.