The two things a client actually needs to do on a spec sheet are ask about a line and say yes. Both happen on the share link, with no account.
Comments land on a specific thing
A client can comment on an individual item or on a whole section, not just on the document. "Is this the brushed one?" attached to the faucet row is a question you can answer; the same question in an email thread is a question you have to go find.
Every comment is timestamped and attributed to the name they typed. They show up in your activity feed on the project, and you get an email so you are not polling the page.
Approval is a record, not a signature
Approving asks the client for their name, then freezes a complete snapshot of exactly what they approved: every item, every field shown to them, and the tier they had selected. It records the timestamp on the server, not on their device.
This is deliberately not an electronic signature. It is a documented, server timestamped acknowledgment trail, which is what protects you in a "you never told me that" conversation. When you need a legally weightier instrument with intent and consent captured, that is a change order.
Changed since approved
Once a sheet is approved, any later change flags the sheet as changed since approval, and you can see what the client actually agreed to versus what the sheet says now.
That indicator is the thing to look at before a trade orders anything. An approved sheet that has drifted is exactly the situation that produces a wrong order.
The activity feed
The project carries a feed of client activity: comments, approvals, board reactions, and trade acknowledgments. It reads newest first and is the fastest way to catch up on a job you have not looked at in a week.
Turning it off
Comments and approvals only exist where sharing is enabled. Disable the share link and the public surface goes away, comments included. The records already taken are kept.
Availability
Comments and approvals are available on the share link on every plan that includes sharing. See pricing.