Not true any longer. As described in http://mercurial.808500.n3.nabble.com/named...

michal8181 on Jan 8, 2014 | parent | context | favorite | on: Scaling Mercurial at Facebook

Not true any longer.

As described in http://mercurial.808500.n3.nabble.com/named-branches-vs-book...

> We have users with thousands of named branches in production and have > done tests on up to 10k branches and the performance impact is fairly > minimal.