They might not be worth spreading to some cities if you're going for a domination win but if you want to win by space race then boosting your main production cities hammers and food to run more engineer specialists could really help with making the parts. And if research rate is the limit on how soon you can launch, then building the corporations that give extra beakers in your Oxford city could make a big difference. It all depends on the % multipliers to beakers and hammers and how much you can cut maintenance costs.Well, while I understand how it can be beneficial at home even if it cost money to maintain, I still don't understand why one would want to expand corps abroad. The creation fee in a city of a neighbouring civ was around 275g (so I guess more if you send your executive farther) and given that at the time of corps the game is usually almost finished, I hardly see a point in spending shields for the executive and money for the creation of the corp for so little benefit, if any.
.
If you have a friendly colony or vassal who will trade techs with you, then you might want to boost his economy or research rate.