Home plumbing repairs are almost always best left to a professional, as trying to fix even one small problem on your own can lead to major plumbing disasters, either at the time of the repair or after the work is seemingly finished. Note a few of those small plumbing repairs that may be more complicated than you realize, and why you want to call a plumber to have them done.
Installing new pipes
If a section of pipe in your home is damaged in any way, you might assume you can just replace it with a similar pipe of the same size. This may not work, as removing the damaged pipe can mean moving the connecting pipes out of place. Plumbing pipes need to be installed at a certain angle so that water and solid materials can move through them properly; if you don't know how to return those pipes to their original angle, this can mean future clogs. Over-tightening connectors, not tightening them enough, not using a sealant, or using the wrong connectors can also lead to water leaks and subsequent damage to the home. For these reasons, leave the installation of any new pipe to a professional.
Installing a garbage disposal
One reason a garbage disposal is complicated to install is that the job involves both electricity and water; if you don't connect the pipes properly and there is a leak, this can cause a short of the electricity. If you don't wire the disposal properly, this can mean added wear and tear on the motor every time you use it. If the disposal slows down because of either plumbing or electrical issues, this can mean the risk of added clogs in the pipes over time.
One reason to never address persistent clogs on your own is that they are often a sign of damage to the pipes, and those pipes should be inspected by a plumber, to address any such damage. Also, if your home has persistent clogs, this usually means your methods of addressing them are ineffective! Adding more chemicals, trying to tackle the pipe with a snake, using a plunger, and other such methods of addressing clogs can actually mean causing damage to the pipes, if these methods are not fixing those clogs properly. A plumber can figure out exactly why your home's plumbing is always clogging and then suggest a permanent fix, such as sound blasting, adjusting the plumbing pipe angles, or replacing the pipes with something of a more appropriate size.