It's part of standard base security protocols, even during non-alert times.
Patrolling is sort of where [snip] soldiers spend most of their duty time.
You've not been on many bases, have you?
Security Forces and Military Police are the ones who drive around bases in cop cars and try to catch people speeding. Those same personnel are going to be checking ID's and credentials at the gate(s), if the job hasn't been farmed out to private contractors. "Perimeter patrols" aren't really a thing, at least, not in the way you're describing them. Certain portions of a base might be under tighter security, such as the flight line of an Air Base. In some bases, (Joint Base Balad being a notable example) perimeter security is going to be handled by sentries in guard towers.
Your typical "soldier" (I assume you mean infantry types?) spends most of his time training or doing some additional duty to keep his unit running smoothly. Unless, of course, you mean in a "deployed" or combat environment, in which case what the soldier spends most of his time doing is entirely dependent upon which type of unit he's in.
Edit: Typos; clarification.
Edited by Yoshiyahu, 10 April 2014 - 08:28 PM.