Hi,
I am not a professional on layout design, however, I know from my advisor that once he adviced me to put dummy transistors at the beginnings and alsı at the ends of each line. So the real transistors located in the middle. I think this is related to matching all the nodes of the transistors. For example in your illustration, if transistor D and E are intended to be matched, although they are at the same sizes they are not matched exactly. Because left of the transistor D is blank but transistor E has neighbours at both sides. So the impedances that are seen by the nodes of D and E are different. If you also add a dummy transistor to the left of transistor D, D and E would be better matched.
All in all, I think it is better to add some dummy transistors at both sides.