Database is a common of important data and we must have redundant server for database server 
or backup data with mysql replication we can backup data to other database server , why i said backup data because we can replicate data which reside in database server to another database server , so if database server fail we can redirect application to database backup manually.
Beside that mysql replication can help us from security side. Hmm…. security ? yes security , ok i will give u example , in mysql replication we know system master or slave , slave replicate data from master. Now please try to imagine if u have 5 server , one master and four servers as slave , with these condition we can set data just insert data to master server and aplication just select or read at four slave servers. so we can limit access write from application side but this system will be useless if application side need write to database servers too, but this system can be distribution of the burden for write or read process.MySQL replication have lack of with data consistency because mysql replication still asyncronous 
but in mysql 6.0 mysql replication will be semi-asyncronous .
If u need replication with syncronous data u can use mysql cluster but i never use it , may be someday , i hope so .Now i will not explain about mysql cluster , ok if u want to try configure mysql replication u just run some steps but i will not tell to you because u can visit this links mysql replication or u can read mysql manual 
may be later i will be write it , but if u don’t have server for implement it u can try with mysql sandbox . I have read from mysql manual , in this manual tell us some advantage with mysql replication like below ( i take from mysql manual) :
The target uses for replication in MySQL include:
* Scale-out solutions – spreading the load among multiple slaves to improve performance. In this environment, all writes and updates must take place on the master server. Reads, however, may take place on one or more slaves. This model can improve the performance of writes (since the master is dedicated to updates), while dramatically increasing read speed across an increasing number of slaves.
* Data security – because data is replicated to the slave, and the slave can pause the replication process, it is possible to run backup services on the slave without corrupting the corresponding master data.
* Analytics – live data can be created on the master, while the analysis of the information can take place on the slave without affecting the performance of the master.
* Long-distance data distribution – if a branch office would like to work with a copy of your main data, you can use replication to create a local copy of the data for their use without requiring permanent access to the master
mysql replication can be one solution from mysql-ha too, depend ur necessary . Welcome to try mysql replication 
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