I'd say fdisk away ad0s3 and use growfs
to enlarge ad0s2 to fill that space.
I usually use Knoppix+QTParted for my resizing needs but it does not support UFS1/2
So i can't say about the safty of growfs.
Depending on the size of ad0s3 and ad0s2 you might want to format it fat16 or fat32 to use it for storage or recovery.
i.e. ad0s3 mountpoint: /recovery a place to stick backups in a seperate partition. Or
ad0s3 mountpoint: /storage a place to stick your music collection or something.
A partitioning sceme I'd like to try when I can reformat an old computer is a root, user, backup, and logging slices consisting of slice1 / + swap, slice 2 /usr, /home, maybe more swap, slice 3 /Backups, and Slice 4 /var, /tmp, + swap. So areas /w higher writing will be towards the ends along /w swap space and keep the more execution/reading parts of the system thoared the middle of the disk.