The procfs manpage states that
procfs is required for the complete operation of programs such as
w. I want to mount it but wonder if there are any security implications of doing this.
This is basically standard in the linux world..
I would assume for that reason, you have not to worry about security implications for this particular question..
What do you expect a security implication could be???
/proc maintains and shows simply an open heart to the kernel and process's
Note: i just "quickly" checked online ( yes i have the internet :P ), and found 2 security problems from 2000 & 2005 for BSD variants... However im sure they are fixed
In my experience in FreeBSD you'll only need to use procfs when you use Linux binary application.
You can check this article on FreeBSD Handbook , hope it helps.