There are typically two reasons you are here, the most common being that you are currently experiencing a blocked sewer line. If this is the case you have multiple drains that are clogged, or multiple backed up drains. If this is the case, more often than not a sewer line cleaning is in order.
This service cleans out the larger pipes in your plumbing system that can be causing several drains in your system from becoming clogged, as a backup down the line can affect multiple drains that feed into it.
The other is preventive maintenance. After years and years of use and abuse, plumbing systems can go through literal tons of water and debris, it is best practice to get some preventative maintenance done. By getting your drains cleaned and a sewer line cleaning, you can know the exact condition of your plumbing system and know that it is not going to get backed up on you!