The answer is long, nuanced and outside the scope of this particular thread, so if want to discuss more, please open a new thread so it get proper title, but to summarize
considering everything is a "rule of thumb" and may have particular exception.
1/ dimensions on B/S accounts increases (possibly a lot) the number of transactions on the system.
This can lead to performance issues, and since there are all kind of automated processes posting on B/S accounts (revaluation, VAT payment etc.) can cause these processes to either generate very large number of transactions or fail completely.
2/ B/S accounts do not get clear at year end, so the multiple balance combination just keep increasing from year to year, and the problem keeps augmenting
3/ From experience upon closer look, many of stated requirement to have dimensions on B/S accounts (such as keeping separate legal entitiies in one company etc.) do not really work for other reasons, making the dimensions just a liability with no value.
4/ there are many operational hurdles that makes recording transactions with the presence of dimensions difficult, such as the defaulting issue on this thread, but also when for example settling invoices with payment etc.
5/ from personal observation, the few clients that ended up putting dimensions on B/S accounts lived to regret it a lot, and some ended up spending a lot of effort (=money) on removing them.