I disagree to a certain extent. In the same way you never know what a ride feels like, you never know what an episode will 'feel' like when watching it. A script and the live performance can be very different.
I suppose with familiar characters likes Clara you can imagine how she would say things, although with The Doctor's lines Capaldi will have a different way of performing those compared to Matt Smith, or David Tennant, or the other 9 doctors.
It depends really on how much you want to be spoiled. The main episode plot doesn't really damage the rest of the series, as most episodes are standalone. Reading story arcs though can spoil a lot.
It's interesting because I've seen big debates on other forums about whether reading a script ruins to excitement and mystery of an episode. As always at the end of the day it's down to a matter of personal opinion.