If I'm buying a Spanish property can I save on taxes by creating a company?

In some cases, yes.

Example:

Stan is a resident of Spain and earns a 100,000 salary from outside Spain. Stan has two choices:

Pay personal income tax in Spain (if he's paying income tax elsewhere then this can be reduced). Stan is in the 42% income bracket, so he will pay around 40,000 euros.

Establish an SL, and the SL pays him. Stan's company pays a corporate tax of 30% (after the first three years, this rises to 35%).
However, corporate tax deductions are extensive in Spain. Stan deducts housing, car, and food for 50,000 euros. 30% of the remaining 50,000 euros is 15,000 euros, so the savings are well worth the costs of SL creation and accounting.

With an SL, there are more options: money that Stan doesn't plan to spend in the near future can be put in the company reserves, making it nontaxable.