What does DocSend do well? I couldn't work without Docsend. The ability to send links to docs and update the documents in the background is insanely useful. Knowing when someone has looked at the information is also helpful for creating new content and the control over the links (ie. being able to turn them off is great). The interface is easy to use and well-explained. I recommend it to everybody.
What does DocSend not do well? I only have three small issues with Docsend. First, when I open my docsend dashboard it always opens to the middle of my folder hierarchy. I can't figure out why. I would assume that when I log in, it would open to the top of the hierarchy. Secondly, the download button is not super visible for viewers. I have taken to sharing a link and explicity describing that if they wish to download the button is on the top right. Third, some of the corporates that we work with can't seem to view docsend docs at work. I know that docsend has limited control over this, but it's worth noting.
What do you wish you had known about DocSend before using? I would tell any new user to think about their link strategy. i.e. are you creating links that are person-specific, company-specific, etc. There is a balance between getting high-resolution info about who has viewed the documents and being overwhelmed with links.
Have you used a competitor to DocSend? If so, how does it compare? The only competitor that I have used is sharing docs with dropbox links. Docsend is far, far superior. It feels more secure, easy to control - and critically you can update the documents.