A small disadvantage is, that it doesn’t work as simple as for example Microsoft Excel. In Excel it’s one step: Select the row, or cell, and activate Frees Panes. The work-around involves 5 steps, I didn’t mention the synchronize horizontal scrolling.
I would like to select a row, right-click and freeze above, or freeze under. (or insert a small narrow separator)
The big disadvantage is that big gray separator. It’s not nice, and it’s sometimes hard to see where a header is pointing to.
(See example: https://postimg.org/image/4wypfpqz5/)