SQL stores relational database whereas Azure Tables stores the non-relational database of massive sizes.
In terms of scalability, Azure Table is more scalable than Azure SQL.
Talking about Queries, Azure SQL has no limitations but in Azure table, you are restricted to only 1000 queries.
Coming to the cost, Azure tables cost $0.00036/ 10,000 transactions and around $0.075 per GB/month.
For detailed Azure SQL pricing, click here.
So, there is no defined answer to when to use the Azure table and when Azure SQL. You just need to know what works for you and your requirements and the data you have.