This is a very complicated question. The first thing I will do is direct you to an excellent website where you can read up on TIC issues: http://www.andysirkin.com.
The disadvantage is that you are not the sole owner of your unit. If you purchase a condominium, you are the one and only owner, the only person on title, and the only person on the loan. If you purchase a TIC, you are on the title along with the other owners of the other units in the building. You essentially own a percent interest in the entire building with a right to occupy your unit.
The other disadvantage is the financing. In the past, your only option was a group loan, where you are on the loan with the other owners in the building. Now there is also the fractional financing option, where you can have a seperate loan, but the cost of these loans is usually about a percentage point higher than a regular loan.
As far as legal issues go, you just want to be sure there is a good TIC agreement.
There are also advantages to purchasing a TIC, the biggest being that it may get you into a neighborhood or a unit you otherwise could not afford to live in. It is a form of affordable housing that San Francisco really needs.