^ exactly..
While I am a fan of longer lease times in my setup, why would you want more traffic for no reason.. I think I have my lease currently at 7 days..
Lets say you have 200 IPs to hand out.. How many clients do you have? If only a few it shouldn't ever be a problem, even if you had a 2 hour lease, and some box was off for 6 months.. Now if you have in total 210 clients, then yeah you can have problems if your leases are too long, or you could get clients switching Ips.
Once a device gets a lease, it should maintain that IP going forward, since it will just renew it at the 50% mark of its lease..
And lets say you turn that off for long time, when it comes back that lease should still be there even if it expired and the client should get that same IP back, even if doesn't specifically ask for that IP in its request..
The only time you could see a problem is if you have a bunch of clients, more than your pool size and you have some lease that expired and some new client comes on and the dhcpd says oh shoot I don't have any free leases, let me start handing out expired leases..
Normally dhcpd will run through all its free leases before it starts to look into expired leases to re-issue.
You should notice this as your IPs either count up from the low end of the lease 1, 2, 3 etc.. or it counts down 254, 253, 252 etc.
One problem I can see with really long leases, is client normally not going to get any changes or new things you might of added to the dhcp scope.. Lets say you had a 30 day lease, and you say changed the dns server your clients should use.. Possible you have clients that don't get that new info for 15 days..
Also I am a fan of reservations - if I want to make sure client X always has 1.2.3.4, I just set a reservation for that client. Doesn't matter if he off 1 hour, or 30 days.. That client will always get 1.2.3.4 from the dhcpd.. And the dhcpd will not hand that IP out to anyone else..