If you want to use OS 3.5 or 3.9, yeah. Otherwise, probably not. Although, with a Blizzard you can softkick 3.1. This is illegal, though.
Is it really illegal though?
I own an A1200, I have a licence to use the 3.0 Roms. Would the copyright owners really begrudge me softkicking the 3.1 Roms, the difference being just a few buigfixes?
In PC land flashing your motherboard bios is offered as 'support'.
In Amiga land, updating your kickstart by a minor revision is 'illegal'.