Single vs Joint Agreement??

I'm signing on a group of tenants who all previously know each other.

What are the disadvantages of signing them on one lease designed for multiple tenants?

Disadvantages? The only disadvantage to a joint and severally liable tenancy agreement would be that you may have to do an addendum if you allowed one tenant to leave and the others to stay.

You should use a joint agreement (one that says all tenants are jointly and severally liable) for several reasons. Advantages:
-You can chose any one or all of the tenants to go after if they default.
-You can accept one full payment for rent from any one tenant.
-All the tenant are responsible for all the clauses of the lease. (So if one violates the lease, the others are responsible too. - Peer pressure!)

Disadvantages of using separate agreements for each tenant:
-If one or more tenants leave, the rest get to stay by paying only their share. The property can be rented for 3/4 or 1/2 the rent level this way.
-You can only hold the one tenant liable for violations or damages. If you don't know which tenant did it, who will you charge?