Most Weston homes have plastic drain lines that don’t corrode or narrow the way old cast iron does, so when a drain clogs here the cause is almost always what went into it, not the pipe itself. Grease that cooled and hardened, coffee grounds, fibrous food scraps from a garbage disposal working harder than it should, and hair combined with soap scum in a bathroom are the usual suspects, sitting at a low point, a fitting, or a trap where flow slows down enough for buildup to catch.
A single fixture backing up is almost always local to that line. Multiple drains backing up at once, especially the lowest one in the house, points further down the system, toward the main line rather than one sink or tub, and that changes what tool the job needs.