Lining the bed with hardware cloth might or might not be worth the trouble and expense depending upon the number and kinds of digging pests that frequent the area.
Moles are among the most common. They often enter raised beds, apparently attracted by the light, eminently diggable soil usually found there. Their digging may disturb seedlings and uproot transplants but moles do not harm root crops. Plant damage is incidental.
Pocket gophers feed on root crops and their mounds and tunnels are intolerable in a vegetable garden. If pocket gophers are common in the vicinity, hardware cloth protection is advisable.
Voles can be very destructive in vegetable gardens but their burrows are of little consequence and in any case hardware cloth protection would not exclude them. They usually enter raised beds at the ground level and damage root crops and other vegetables mostly at or just below the soil surface.
Hardware cloth under a raised bed limits or precludes working the soil beneath. Digging deeper is sometimes beneficial depending upon the kinds of plants to be grown there.