We have studies since ages ago that consistency in code style is one of the most important requirements for code quality.

This goes down to the details like that you should either use spaces over tabs OR prescribe editor config such that the code looks similar on each machine.

Of course this doesn't automatically mean that code ligatures are harmful, but I would be quite wary of using them. At the very least it introduces some friction, not sure if the arguably lower mental load of using real mathematical symbols instead of the ASCII symbols makes up for it.