Q:

Why is 32bytes the default ping size? Is it okay to use less?

I have a very large number of addresses I need to ping on a company network. I want to be as unobtrusive as possible. Would using ping 1.1.1.1 -l 1 reduce the strain on the network? Is the difference between 32 and 1 even worth the trouble? Is there a reason 32 is the default?
I suppose it is worth mentioning I am on a windows box and using PowerShell.

A:

Ethernet has a minimum frame size of 64 bytes. If you try to send less than that, your system will pad it to 64 bytes anyway, if it's being sent on Ethernet. Ping already sends close to minimum-sized frames:
14 bytes of Ethernet header
4 bytes of Ethernet checksum
20 bytes of IPv4 header
8 bytes of ICMP header
= 46 of 64 bytes, so using an 18 byte payload should give you a minimum sized frame, if I got my facts and arithmetic right. 
Wi-Fi doesn't have a minimum frame size, so if your pings are going over Wi-Fi, a zero-length ping payload will use slightly less airtime. 
I'll also note than even if you were saving a full 32 bytes on each of 9000 pings (and 9000 ping replies), that all adds up to only half a millisecond of gigabit Ethernet bandwidth. You've wasted far more of your company's resources on your salaried time thinking about this.

