Important Points to remember about Salesforce Sandbox Limits as per Edition:
Important Points to remember:-
1) If you need licenses for more sandboxes, contact Salesforce to order sandboxes for your organization.
2) Sandboxes don’t send email notifications when storage limits are reached.
3) Change sets are not available to Professional Editions.
4) you can’t save new data in your sandbox if sandbox reach storage limit.
5) To check your storage limits, Goto Setup -> Storage Usage in your sandbox.
Reference – https://help.salesforce.com/articleView?id=deploy_sandboxes_limits.htm