Erstwhile, watchmakers tend to use heavy and big balances. That big and heavy that the mainspring energy available was just about sufficient to ensure a satisfactory amplitude. That means that the mainspring barrel (energy storage) has to be in due proportion to the balance, and additionally, both have to fit into a movement of a given diameter.
A preferably big and heavy balance (= maximal radius of gyration) was chosen because this ensemble is more resistant to external parasitic drag than a smaller and lighter balance which oszillates at the same frequency.
In the 1950 years of the past century the watchmakers broke new and better ground with the development of high-beat escapements. They provided the same stabilising effect on the rate as the previously described greater radius of gyration. Since fast-beating balances are much lighter than their slow-beating heavy cousins, the oszillating system is much less susceptible to positional errors.
Pivots of smaller diameter can be used, which in turn results in better performance in horizontal or vertical positions.
The not unimportant question is: Is the technically superior solution always the most beautiful? For the VA I chose the classic way: that means a big balance and a voluminous mainspring barrel. At the risk of being not absolutely up to date.
