Yes, there is a distinct disadvantage. Leaves gradually lose their ability to efficiently carry on photosynthesis as they senesce. These leaves are normally replaced by new foliage which comes on line perfectly tuned to prevailing light levels. Persistently removing the new growth of higher plants to maintain a constant outline can cause serious decline or even death. Another consideration is, as the wood within the outline senesces it becomes increasingly reluctant to back-bud.
Like almost all other bonsai practitioners, I had to learn the hard way that persistent removal of new growth to maintain a tree's eye appeal will not end well. Woody plants need time to recover from pruning. Often, when a tree is prepared for a show and made to look perfect, it is allowed at least a full year of growing wild before being pruned again.
Too, most species of Thuja, and occidentalis in particular, are well known to be weak back-budders. If you need to build a hedge as an example of what your system can do, you'll need to depend on back-budding for the new growth, inevitable if you hold to a precise outline, try T occidentalis 'Zmatlik' if you can find it. Iseli should have it. I believe they were first to commercialize it.
Al
