I really like that I can set up recurring invoices for my monthly clients, and that the invoices ship out on the correct day ensuring that I get paid in a timely manner. I also enjoy the monthly expenditure tracking that is included in this web app.
Sometimes the history for a specific client is difficult to target, especially when someone wants to see their yearly expenses with me.
This is a great accounting application (AND it works with the Station app!!) for small business. It is very flexible until you link a bank account that is not your primary account for business income and expenses. I would definitely only link it to your business account, and not one that is used for other purposes. I had to reset mine this year because it got a little confused between my personal and business accounts. I'm certain it was operator error, and I did not utilize their help feature before that. Aside from that, Wave has been working flawlessly, and I do recommend it for small business.
I primarily use Wave for all of my small contracts for design work, and all of my larger monthly retainers. Giving my clients an option to view their invoices and make payments online is a serious bonus. Also, keeping track of expenses vs. income is an important part of running a small business. Wave has not let me down yet!