For most basic client actions, having a Bonsai account is not at all a requirement.
These include actions like:
Accepting a proposal
Counter-signing a contract
Paying an invoice (with the exception of setting up an auto-pay invoice)
Viewing my project, paid timesheets and reporting
As a client, you really only need to create a Bonsai account if you are using Bonsai as a means to manage subcontracting. Actions such as...
Creating projects to invite subcontractors to
Viewing your total spend across projects
Sending secure files and messages on projects
Adding/managing subcontractors with custom onboarding flows
Sending a custom contract to a subcontractor