If you have a small business with few transactions and simple bookkeeping requirements, Wave will be ok.
As your company grows and your requirements become more complicated, it's worth it to switch to QuickBooks.
If you're not sure whether your company is too big for Wave or not, it probably is or will be soon.
Getting your business in to QuickBooks sooner rather than later will ensure you're prepared for the next growth spurt. Grandma was right when she said "you'll grow into it!"
Wave is free, but it could end up being more expensive in the long run. How much is your time worth? If QuickBooks could save you an hour a month, would it be worth $40/month? What about two hours? The point is this, your time is worth something.
Smart money management is not about paying the least amount for everything. It's about paying the right price for the right service at the right time.