Yes. A good use case for this, and the example I'm going to use, is when you have an Item price, but want to have the option to override the list price.
[My List Price] is a field coming from a parent table, or an items table.
[Price Override] is a field that can change the value
[Price] will be the formula field that takes the list price, or take the override price.
[Price] formula would be:
If( IsNull( [Price Override] ), [My List Price], [Price Override])
If you are using text fields, the similar, but use the sign ="" rather than the null:
If( [My Override Text]="", [My Default Text], [My Override Text])
