some of the top benchrest shooters in the country shoot with their bullets touching the lands of their rifles.reference any of the precision shooter compilings dealing with benchrest accuracy.
when fire forming wildcat cartridges, proper case dimensions to mirror chamber dimensions can only be achieved this way as there are no factory cases to start with.
if you use extremely slow burning powders (slow for the cartridge you are using) you can use compressed loads safely. BUT, you should always work up loads slowly checking for pressure signs.
the only problem i could see is if you are shooting large capacity cases that demand the slowest burning powders to begin with.