SQL LOADER help

Hi Team,

I have created  the below control file for loading mutliple files at one shot using SQL LOADER , this script I have taken from one of the blog on sql loader.
My Question is  
1. does SQL LOADER load all the 3 files simultaneously into the target table daily upload , if so how this processing happens and how many files does SQL LOADER read at a time and also the rows
2. Impact on the indexes if any.
 

load data
infile 'data_daily1.csv'
infile 'data_daily2.csv'
infile 'data_daily3.csv'
append
into table daily_upload
fields terminated by ","
optionally enclosed by '"'
trailing nullcols
(
col1,
col2,
col3,
col4,
col5
)