This is only advisable if the input data will fit into the available memory without compromising other processes at the same time.
You don't want the system to start paging heavily or exhaust memory just for the sake of having all data in memory at once.

Slurping files can sometimes be advantageous.
Other times using read() or sysread() to read large blocks of data might do the trick.
Personally I still find myself using a simple  while (<FH>){...} for most jobs, from logfiles to multi-gigabyte datasets.

Cheers,

BazB