5-Bromo-2-fluorophenol carries three very different features: An -OH group. A bromine atom. A fluorine atom. And each can play a different role. The -OH group can act as one connection point, allowing chemists to attach another molecular fragment through oxygen.
The bromine can provide another. Modern cross-coupling chemistry can replace it with a completely new piece of molecular architecture. Fluorine often does something different: it stays.
Global Chemical Database