"does this not benefit the UK in that, lengthy terms (years) of training and associated costs are avoided?"
For trained folk, only in the short term; and detrimentally it continues the idea that one need not bother accepting the responsibility of training the necessary skills we need, as they can be taken from other nations that need them and who have trained them.
Furthermore the benefit is hardly as beneficial as one might hope since they will have taken the available jobs while those unemployed here who are left untrained still need supporting from the taxpayer; so we've lost the chance to reduce the welfare budget on top. Buying in labour should be a desperate, and guilt ridden, last option, always avoided whenever possible.