What are the disadvantages of microform catalogue?

There are more advantages than disadvantages, but the most glaring disadvantage is that if the internet, or the servers, or the computers are down, you can't find specific books.

Most libraries have a back-up card catalog, but it's tedious and usually requires the assistance of a library staff member.

You can find general subject areas if you can refer to the call number scheme, but finding specific books is nearly impossible.