I want to know if it is possible to create custom fields only once and use them through out multiple entities. For instance if I want to have a field called "Partner" and have it in Leads, Opportunities and Account. Can I just create the field only once and have it accessed in three different entities?
Thanks in advance
Yes and no. You'll need to create the field on each entity but you can share the data between them.
One way is a shared option set. This lets you manage one list of items and use it over and over on different entities. Another way you could go about it is to have a new entity for the data you're storing, and instead of creating a field you create a lookup to that record. This would be good if you had a list of countries that you wanted to reference all over CRM.