In addition to reducing team effectiveness for a period of time, adding people to a team faster than once a month slows assimilation. When team assimilation is slowed, there’s a risk of damaging team cohesion. When a new member arrives to your team, it’s great to help them technically by answering questions about the code base etc., but where we as engineers often fail is the social aspect of making them a team member. Maybe your team goes out to lunch together on Thursdays, make sure you invite them to this outing on Tuesday. Maybe you have other social rituals, make sure they’re included. When you understand your co-workers, it’s easier to understand how to have open discussions about things like architecture and coding. Be as open to letting people go who detract from team cohesion as quickly as you would for technical reasons. It’s that important. This doesn’t mean fire people who don’t want to go to lunch with you, but if the team needs to walk on egg shells around a member, that member is probably not worth having around.