The capacitor bank on HT side will anyhow correct the PF,
the line losses will not be reduced. hence by putting the
capacitors on LT side, that too nearer to the load, the
losses and PF can be much better improved. The capacitors on
HT side is just to minimize the line losses, even though it
improves PF putting capacitors on LT side is always
recommended that too nearer to load, so as to get efficient
usage of electricity.
 Please not that this answer is only for inductive load
consideration as linelosses and transformers and most of the
loads conneted to the line is inductive.

If the capacitors are installed in the ht side the pf of 
the line improves but not the plant.And the plant pf is in 
poor condition only which may leads to the losses on our 
side and reactive load on the transformer may increase so 
even if we have capacitors on ht side it is advaisable to 
kept the capacitors on load side also.

If capacitor bank is installed in switchyard & capacitors 
are connected on HT side , it will try to balance losses of 
transmission line and not towards LT side, where as for 
maintaining /increasing LT side voltage, we need to install 
seperate capacitors nearer to load so as to maintain PF at 
LT side also depending upon connected load & distance of 
equipment connected in LT side.