What causes "balancing pool" messages ?

[Nomad]

I have two 3.1.0 dhcp servers running and have noticed in my logs these
messages:

Jan 9 04:13:23 DHCP1 dhcpd: balancing pool a854600 172.16.81.96/28 total 9
free 6 backup 3 lts 1 max-own (+/-)1
Jan 9 04:13:23 DHCP1 dhcpd: balanced pool a854600 172.16.81.96/28 total 9
free 6 backup 3 lts 1 max-misbal 1
Jan 9 04:13:23 DHCP1 dhcpd: balancing pool a8487c0 172.16.145.160/27 total
29 free 12 backup 7 lts 2 max-own (+/-)2
Jan 9 04:13:23 DHCP1 dhcpd: balanced pool a8487c0 172.16.145.160/27 total 29
free 12 backup 7 lts 2 max-misbal 3
Jan 9 04:13:23 DHCP1 dhcpd: balancing pool a81b3e0 172.21.1/24 total 123
free 74 backup 49 lts 12 max-own (+/-)12
Jan 9 04:13:23 DHCP1 dhcpd: balanced pool a81b3e0 172.21.1/24 total 123 free
74 backup 49 lts 12 max-misbal 18

For each network segment, I see these messages coming in every minute.  In
case it matters, here's the failover section of my dhcp servers:

#failover definition
failover peer "dhcp" {
    primary;
    address 172.16.100.10;
    port 520;
    peer address 172.16.100.11;
    peer port 520;
    max-response-delay 60;
    max-unacked-updates 10;
    mclt 300;
    split 255;
    load balance max seconds 3;
}

#failover definition
failover peer "dhcp" {
    secondary;
    address 172.16.100.11;
    port 520;
    peer address 172.16.100.10;
    peer port 520;
    max-response-delay 60;
    max-unacked-updates 10;
    load balance max seconds 3;
}


And by the way, what does the "lts" mean in these messages?
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