Reinforce a strong or shielded teammate and you can keep them a secret until you have enough troops to stand on your own. It is not just a tool for combat however, as you can use it to hide a build up of troops or just keep them safe. After a successful hit you can much more safely follow up with a rally. If you have a couple castles in your hive like this and everyone with anti-scout, it becomes a very dangerous hive to attack. If your hive keeps falling under attack by an opponent too strong for your hive, you can reinforce a team member when not under attack and then just let them be found. If you wish to hive, reinforcement is a key tool to take advantage of. Your opponent only sees caravans, not the amount.
The same can be said for sending resources. If the castle has prisoners you don’t want freed, reinforcing him with the help of your guild can prevent that from happening and bait opponents into a trap. It does not modify the might of the target castle, which means they can be underestimated with proper use of anti-scout. It is a castle of low might or level with a high quantity or quality of troops typically seen in higher might and level castles. It is the ability to send an army, with a leader, to place a camp in front of your target’s walls to intercept the enemy. It is the ability to send troops into a guild member’s embassy from multiple other members of the guild, placing them under the command of the castle’s leader to use their stats.