General rules for choosing sh or SaaS - odoo-ps/psbe-process GitHub Wiki

Cases where we force the use of SH:

Customisations that take at least 10 hours
The customer has reached at least 10 hours on previous development or will be over 10 hours with the new development request
If you anticipate (or the sales or consultant does) that the customer will need many customization in the future and/or will need customization for which only sh will work

Some modifications of existing fields (remove a compute for example)
Modification of the webshop's business logic. For cosmetic modifications, we can still do it in Saas if it is validated by the expert Nicolas Wisniewski (NWI)
If there are on_change methods on a field and you need to modify these on_change, the only way is with sh as the methods need to be overridden
Modification on controllers (even though it's possible in SaaS, it's painstakingly long)
Any method called automatically by Odoo for which you can't replace with server action. Example: change the behavior of a write or create method

If you decided the customer has to go on sh there can be consequences on the estimation. Here are the guidelines for each case:

your analysis requires some elements (models, fields, views, etc.) from a studio customization => you need to rewrite the studio components needed for your development in python. You need to add the estimation for this rewriting in your analysis
your analysis requires some code or elements from a SaaS module => you need to rewrite the components needed for your development (server actions, etc). You need to add the estimation for this rewriting in your analysis