TCP is a connection-oriented protocol and it requires data
to be consistent at the destination and UDP is
connection-less protocol and doesn't require data to be
consistent or don't need a connection to be established with
host for consistency of data.
UDP packets are smaller in size. Can't be greater then 512
bytes. So any application needs data to be transffered
greter than 512 bytes uses TCP 
We often discuss why services use both the protocols i.e.
TCP and UDP. These services can also realy on TCP instead of
UDP because TCP is a connection-oriented protocol whereas
UDP is connection-less! then why use UDP? 
For example, DNS uses both TCP and UDP for valid reasons
described below. Note that UDP messages are not larger than
512 Bytes and are trucncted when greater than this size. So
DNS uses TCP for Zone transfer and UDP for name queries
either regular (primary) or reverse. UDP can be used to
exchange small information whereas TCP must be used to
exchange information larger than 512 bytes. If a client
doesn't get response from DNS it must retransmit the data
using TCP after 3-5 seconds of interval.

tcp or udp does use both