Valgos is a fairly powerful monster. Keep in mind his high attack, when defending or attacking. Valgos makes for a very good defender, especially against Sabnox or monsters with ranged attacks as he burrows under the earth, making him it impossible to damage him until he is attacking the monster. He also is fairly fast, and can burrow under walls to quickly repel any monsters. When on the offense, Valgos is very good at destroying walls, as he can destroy wooden or brimstone walls in under 5 seconds at level 1. If the base has no walls, using Valgos is an excellent choice, as he obliterates buildings quite easily, and can destroy buildings while other monsters take the hits or loot buildings.
You can also remove undefended Eye-ra bait by using Valgos. (Note: BD blocks take a long time to destroy.)
Map Room 3 Tips
If used in conjunction with Eye-Ras, you can take down the ADTs in a levele 30 resource outpost relatively easily