Does SSL / TLS consume more bandwidth (adds overhead to network communication)?
For most types of transfers adding SSL/TLS doesn't significantly affect network load (about 2% increase based on Google statistics).
However if you use RESTful APIs where the amount of data is small, you need to ensure that persistent connection is used, otherwise with small request bodies SSL will add significant overhead. The overhead would differ depending on certificate size and number of certificates in the chain but if you have to establish SSL session to send a 200-byte request and receive a 2-Kb response, SSL handshake can add another 5-7 Kb easily, so the overhead is quite significant (especially for mobile devices).
Also in command-response protocols (eg. SMTP, FTPS) where commands and responses are rather short the overhead of TLS packets that wrap the data is much larger than the average 2%.