Optional unless the letters f and i collide

Lig­a­tures were invented to solve a prac­ti­cal type­set­ting prob­lem. In the days of metal fonts, cer­tain char­ac­ters had fea­tures that phys­i­cally col­lided with other char­ac­ters. To fix this, font foundries cast lig­a­tures with their fonts, which com­bined the trou­ble­some let­ters into one piece of type.

The most com­mon lig­a­tures involve the low­er­case f because of its over­hang­ing shape. Other lig­a­tures also exist—some prac­ti­cal, some dec­o­ra­tive, some ridicu­lous.

Dig­i­tal fonts don’t have phys­i­cal col­li­sions, of course, but cer­tain let­ter com­bi­na­tions might still over­lap visu­ally. The only time lig­a­tures are manda­tory is when you have an actual over­lap between the let­ters f and i. Check this com­bi­na­tion in the bold and italic styles too.

Beyond that, lig­a­tures are largely a styl­is­tic choice. To my eye, they can make body text look some­what quaint or old-fash­ioned. If you like that look, great. I don’t. So unless char­ac­ters are actu­ally col­lid­ing, I gen­er­ally keep lig­a­tures turned off.