Debris flowing down a downspout drain that has been foolishly connected to the building foundation drain system can block that drain leading to basement flooding from either.
Gutters going into sewer.
I assumed storm but if you re talking the sanitary sewer you re just making more work for the treatment plant.
The lawn is fine but make sure you divert it well away from your foundation.
A rain gutter drain pipe is usually installed to carry water away from your house.
If the water backs up into the gutter there is a blockage in the pipe.
An underground drain pipe can become clogged in a variety of ways including leaf buildup or damage to the pipe itself.
Many of these pipes are placed underground to avoid the eyesore of pipes laying on the ground next to your house.
Spraying high velocity water from a hose blowing high pressure air from a pump or vacuum or using a pipe snake can often clear it.
This can be done by running water from a hose down into the pipe from the point where it meets the gutter.
Most homeowners get this and keep their gutters clean and flowing.
Can rainwater from guttering discharge into combined sewer system.
Debris flowing down the downspout drain leaves from gutters can block floor drains or even the main building sewer line leading to sewage backups into the structure.
For example homes have rain gutter systems to collect and channel rain water off the roof into a downspout instead of simply allowing it to pour over the edge where it will saturate the soil in the 10 foot zone around the home and ultimately end up in the basement.
Wait sanitary or storm sewer.
The rain is going into the sewer pipe normally i don t see how the rain off your roof would help anything.