They're not completely identical. In cases where it matters, the redirection approach will generally give more annoying and obscure results (of course that might be what you want though).
$ cat < /proc/self/maps
$ cat /proc/self/maps
55c61257e000-55c61258a000 r-xp 00000000 fd:00 1180143 /usr/bin/cat
...
Or try grep, the search program
$ grep "grep" /proc/self/exe
Binary file /proc/self/exe matches
$ grep "grep" < /proc/self/exe
$
Bit of a cheat, but you're most likely to run into this when using `sudo`, to run commands with `root` access:
$ sudo cat < /etc/shadow
bash: /etc/shadow: Permission denied
$ sudo cat /etc/shadow
root:!::0:99999:7:::
....