When your quote triggers excessive header and line-item approvals you will receive a SOQL limit error. While some of the below numbers are firm, others, which are highly dependent on system performance and configuration complexity, are suggestive, having been tested in a "plain vanilla" test implementation. Depending on how complex your configuration and setup are and how much customization is involved in your org, a SOQL limit error becomes increasingly likely when you exceed the following numbers:

Approval process

Number supported

Total number of records that can be submitted for approval

Up to 50 records (the submitForApprovalsBulk API supports up to 50 context object records.)

Total number of records that can be canceled for approval

Up to 50 records (the cancelApprovalsBulk API supports up to 50 context object records.)

Total number of approval requests supported per unique user

Up to 35 approval requests

Total number of line items supported that require approvals (assuming each line item requires all five levels of approver sequentially)

Up to 35 line items

Total number of approval requests supported per quote

Up to 225 approval requests

Total number of child process (line item-level) approval requests supported per quote

Up to 175 approval requests

Recall and resubmission limitsThirty-five line items with five-level approvals in a sequential format. If four levels are approved, recalling the quote produces a SOQL error on resubmision.
Total number of approval requests submitted in asynchronous modeUp to 300 approval requests
Total number of approval requests approved/rejected in asynchronous modeUp to 100 approval requests

For example, if your quote comprises three levels of approval and 20 line items for approval, Salesforce may throw a SOQL error. 

These numbers were tested in a non-customized, out-of-the-box product instance. The time taken to execute these processes will vary based on your Conga Approvals Salesforce instance's customizations.